Dc-coupled high-voltage level shifter

ABSTRACT

Systems, methods, and apparatus for use in biasing and driving high voltage semiconductor devices using only low voltage transistors are described. The apparatus and method are adapted to control multiple high voltage semiconductor devices to enable high voltage power control, such as power amplifiers, power management and conversion (e.g. DC/DC) and other applications wherein a first voltage is large compared to the maximum voltage handling of the low voltage control transistors. According to an aspect, timing control of edges of a control signal to the high voltage semiconductor devices is provided by a basic edge delay circuit that includes a transistor, a current source and a capacitor. An inverter can be selectively coupled, via a switch, to an input and/or an output of the basic edge delay circuit to allow for timing control of a rising edge or a falling edge of the control signal.

CROSS REFERENCE TO RELATED APPLICATIONS—CLAIM OF PRIORITY

The present application is a continuation of U.S. application Ser. No.16/689,916, filed Nov. 20, 2019, entitled “DC-Coupled High-Voltage LevelShifter”, to issue on Apr. 13, 2021 as U.S. Pat. No. 10,979,042, whichis herein incorporated by reference in its entirety. Application Ser.No. 16/689,916 is a continuation of International Patent ApplicationPCT/US18/38123, filed on Jun. 18, 2018 and entitled “Timing Controllerfor Dead-Time Control” which, in turn, is a continuation of U.S. patentapplication Ser. No. 15/627,196, filed on Jun. 19, 2017 and entitled“DC-Coupled High-Voltage Level Shifter”, now U.S. Pat. No. 10,116,297,issued Oct. 30, 2018, the disclosures of all of which are incorporatedherein by reference in their entirety.

The present application may be related to U.S. Pat. No. 9,484,897,issued on Nov. 1, 2016 and entitled “Level Shifter”, the disclosure ofwhich is incorporated herein by reference in its entirety. The presentapplication may be related to U.S. Pat. No. 5,416,043, issued on May 6,1995 and entitled “Minimum charge FET fabricated on an ultrathin siliconon sapphire wafer”, the disclosure of which is incorporated herein byreference in its entirety. The present application may also be relatedto U.S. Pat. No. 5,600,169, issued on Feb. 4, 1997 and entitled “Minimumcharge FET fabricated on an ultrathin silicon on sapphire wafer”, thedisclosure of which is incorporated herein by reference in its entirety.The present application may also be related to U.S. patent applicationSer. No. 14/964,412, filed on Dec. 9, 2015 and entitled “S-Contact forSOI”, the disclosure of which is incorporated herein by reference in itsentirety. The present application may also be related to U.S. patentapplication Ser. No. 15/488,367, filed on Apr. 14, 2017 and entitled“S-Contact for SOI”, the disclosure of which is incorporated herein byreference in its entirety. The present application may also be relatedto U.S. Pat. No. 9,024,700 B2, entitled “Method and Apparatus for Use inDigitally Tuning a Capacitor in an Integrated Circuit Device”, issuedMay 5, 2015, the disclosure of which is incorporated herein by referencein its entirety.

TECHNICAL FIELD

Various embodiments described herein relate generally to systems,methods, and devices for use in biasing and driving high voltagesemiconductor devices using only low breakdown voltage transistors.

BACKGROUND

In applications where high voltage semiconductor devices operating inhigh voltage conditions are controlled, high breakdown voltagetransistors are typically used in corresponding control circuits. Forexample, in traditional gallium nitride (GaN) power managementapplications, transistors such as laterally diffused metal oxidesemiconductor (LDMOS), bipolar or high voltage metal-oxide-semiconductorfield-effect transistors (MOSFETs) can be utilized to control the GaNdevices operating in high voltage conditions. Since these controltransistors typically have poor figure of merit (FOM), compared to theFOM of the GaN devices, which can thereby, for example, limit theoperating frequencies of the GaN devices, the overall circuit (e.g.power management) can be limited in performance by the large, highvoltage control transistors which can be difficult to charge anddischarge quickly (e.g. their FOM is too high) and therefore the benefitof using the GaN devices can be substantially reduced. In addition topower management applications, high voltage signals may be found inamplifiers such as audio amplifiers (especially Class-D audioamplifiers); filter banks; and drivers for resonant circuits; and anyother application in which peak voltages may exceed the voltage handlingcapability of the control circuits being used to achieve theapplication.

This application applies to those circuits with high side (HS) and lowside (LS) controls that either pull a common output node up to a highvoltage or pull the output node down to a low voltage (often a referencevoltage or ground). Such circuits require efficiency, low distortion,high speed, flexibility, reliability and low cost. The currentapplication addresses these issues by addition of dead time control tothe parent application.

In such applications where high voltage devices are controlled, it canbe desirable to tightly control timing of the ON state of the highvoltage devices, so as to, for example, reduce or eliminate overlap timeof the high voltage devices in the ON state.

SUMMARY

According to a first aspect of the present disclosure, a timing controlcircuit configured to control timing of edges of an input square wavesignal, the timing control circuit comprising: a first processing pathcomprising a first plurality of a same configurable edge delay circuitarranged in series connection, the first processing path configured toselectively delay one or both of a rising edge and a falling edge of theinput square wave signal; and a second processing path comprising asecond plurality of the configurable edge delay circuit arranged inseries connection, the second processing path configured to selectivelydelay one or both of the rising edge and the falling edge of the inputsquare wave signal independently from the first processing path; whereinthe configurable edge delay circuit is configured to selectively providean edge delay to one of the rising edge and the falling edge based on anON or OFF state of an input switch of the configurable edge delaycircuit, and wherein the edge delay is based on a charging time of onecapacitor by a current source to reach a trip point voltage of aninverter.

According to a second aspect of the present disclosure, a circuitalarrangement configured to provide timing information for control of ahigh side (HS) device and a low side (LS) device operating in a highvoltage domain, the circuital arrangement comprising: a timing controlcircuit operating in a low voltage domain, configured to control timingof edges of an input square wave signal, the timing control circuitcomprising: i) a first processing path to provide timing information ofthe HS device, comprising a first plurality of a same configurable edgedelay circuit arranged in series connection, the first processing pathconfigured to selectively delay one or both of a rising edge and afalling edge of the input square wave signal; and ii) a secondprocessing path to provide timing information of the LS device,comprising a second plurality of the configurable edge delay circuitarranged in series connection, the second processing path configured toselectively delay one or both of the rising edge and the falling edge ofthe input square wave signal independently from the first processingpath; wherein the configurable edge delay circuit is configured toselectively provide an edge delay to one of the rising edge and thefalling edge based on an ON or OFF state of an input switch of theconfigurable edge delay circuit, wherein the edge delay is based on acharging time of one capacitor by a current source to reach a trip pointvoltage of an inverter, wherein all transistor devices of the timingcontrol circuit are each configured to withstand a voltage substantiallysmaller than a high voltage of the high voltage domain.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent disclosure and, together with the description of exampleembodiments, serve to explain the principles and implementations of thedisclosure.

FIG. 1 shows two high voltage stacked transistors, a low sidetransistor, LS, T1, and a high side, HS, transistor T2.

FIG. 2 shows a prior art embodiment of a gate driver circuit with anon-galvanic coupling (e.g. capacitive) used for controlling the highside of the high voltage stacked transistors of FIG. 1.

FIG. 3A shows a timing diagram representative of a processing of a pulsesignal HX by the prior art embodiment of the gate driver circuit shownin FIG. 2 where a processing delay of an edge of the HX signal issubstantially equal to a pulse width of the pulse signal HX.

FIG. 3B shows an edge detection circuit used for processing of the pulsesignal HX by the prior art embodiment of the gate driver circuit shownin FIG. 2. Also, shown in FIG. 3B, are input pulse voltage signal to theedge detection circuit and a detected edge voltage signal by the edgedetection circuit.

FIG. 3C shows a timing diagram representative of a processing of a pulsesignal HX by the prior art embodiment of the gate driver circuit shownin FIG. 2 where a processing delay of an edge of the HX signal issubstantially equal to a dead-time length between ON states of the LSand HS transistors T1, T2.

FIG. 4 shows a block diagram of a gate driver circuit according to anembodiment of the present disclosure which can be used to control thelow side and the high side of the high voltage stacked transistors ofFIG. 1.

FIG. 5A shows a pulse detection circuit used for processing of the pulsesignal HX by the gate driver circuit of FIG. 4 comprising a parallelresistive-capacitive coupling.

FIG. 5B shows an input pulse voltage signal to the pulse detectioncircuit of FIG. 5A and a detected pulse voltage signal by said edgedetection circuit.

FIG. 5C shows an exemplary implementation of the pulse detection circuitof FIG. 5A where the parallel resistive-capacitive coupling comprisesseries connected resistors and series connected capacitors.

FIG. 6A shows an embodiment according to the present disclosure of theHS level shifter with the parallel resistive-capacitive coupling shownin FIG. 4. In such embodiment, a flying comparator comprisingexclusively low voltage transistors is used.

FIGS. 6B and 6C show variations of the HS level shifter shown in FIG.6A, where charge pump circuits are used to increase voltage levels toinput pulses to the HS level shifter.

FIG. 7 shows details of the flying comparator circuit used in the HSlevel shifter of FIGS. 6A and 6B.

FIG. 8A shows a transistor of the flying comparator with a highimpedance node and a low impedance node with respect to a flyingvoltage.

FIG. 8B shows a clamping circuit provided to protect over voltage acrossthe low impedance node and the high impedance node of the transistordepicted in FIG. 8A.

FIG. 9A shows an embodiment according to the present disclosure where acascode stage is used to allow operation of the flying comparator over avoltage higher than a voltage withstand capability of the low voltagetransistors of the flying comparator.

FIG. 9B shows an exemplary embodiment of two gate drivers operating overdifferent flying voltage domains.

FIG. 10A shows a timing diagram according to an exemplary embodiment ofthe present disclosure of a logic circuit acting upon a differentialoutput signal of the flying comparator.

FIG. 10B shows an exemplary embodiment according to the presentdisclosure of a logic circuit for providing the timing diagram depictedin FIG. 10A.

FIG. 11 shows more details of a common input logic block of the gatedriver circuit shown in FIG. 4, comprising a dead time control circuit.

FIGS. 12A, 12B and 12C show timing diagrams of the high side and the lowside control signals generated by the gate driver of FIG. 4.

FIG. 13 shows exemplary relative timing of control signals generated bythe dead time control circuit of the present disclosure.

FIGS. 14A and 14B show a basic edge delay circuit according to anembodiment of the present disclosure.

FIGS. 15A and 15B show coupling of one or more inverters to an inputand/or output of the basic edge delay circuit of FIGS. 14A and 14B.

FIGS. 16A and 16B show exemplary embodiments according to the presentdisclosure of dead time control circuits using the basic edge delaycircuit of FIGS. 14A and 14B.

FIG. 17A shows a configurable edge delay circuit according to anembodiment of the present disclosure that is based on the basic edgedelay circuit of FIGS. 14A and 14B, with added flexibility toselectively delay the leading edge or trailing edge.

FIG. 17B shows an additional embodiment of a configurable edge delaycircuit, based on the configuration shown in FIG. 17A, with addedflexibility to selectively invert an output pulse.

FIG. 18A shows an exemplary dead time control circuit according to anembodiment of the present disclosure based on the configurable edgedelay circuits (1710A) and/or (1710B).

FIG. 18B shows another exemplary dead time control circuit according toan embodiment of the present disclosure based on the configurable edgedelay circuits of FIGS. 17A and 17B.

FIG. 18C shows an exemplary embodiment according to the presentdisclosure of an edge timing controller based on the configurable edgedelay circuits of FIGS. 17A and 17B.

FIG. 19 shows a current source circuit with compensated current withrespect to process, voltage and temperature variations.

FIGS. 20A, 20B and 20C show different low voltage transistor structureswhich can be used in the various embodiments of the HS level shifteraccording to the present disclosure.

FIG. 21 is a process chart showing various steps of a method forcontrolling a high voltage device capable of withstanding a voltagehigher than a first voltage with low voltage devices capable ofwithstanding a voltage equal to or lower than a second voltage, thefirst voltage being substantially higher than the second voltage,according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

As used in the present disclosure, the figure of merit (FOM) of aswitching transistor (e.g. a transistor which can have a conducting ONstate and a non-conducting OFF state), also simply noted as FOM, refersto the product of the ON resistance R_(on) of the transistor and thegate charge Q_(g) of the transistor. A lower FOM can be indicative of ahigher switching performance of a transistor. Having a low FOM,especially at high withstand voltages, is a distinctive characteristicof GaN transistors, which are capable of handling up to 100 volts with aFOM approximately ten times lower than the FOM of a high voltage MOSFET.

As used in the present disclosure, a low voltage device or low voltagetransistor refers to a semiconductor transistor device with a lowbreakdown voltage which can withstand and block (e.g. in the OFF state)DC voltages (e.g. typically applied between the source and drainterminals of the transistor, or any two of drain, source and gateterminals) less than 10 volts and more typically substantially less than10 volts, such as less than 3.3-5 volts. Some exemplary low voltagedevices are complementary metal-oxide-semiconductor (CMOS) transistors.

It can be desirable to use small, low breakdown voltage MOSFETtransistors which can have figure of merits (FOMs), as measured, forexample, by the product of the ON resistance R_(on) of the transistorand the gate charge C_(g) of the transistor, similar to or better(lower) than the FOM of high voltage transistors. Such MOSFETs can allowfor best use of the GaN characteristics, thereby improving bothperformance and cost of the implementation.

It can also be desirable to allow regeneration (i.e. re-construction) oftiming control information not only based on edges of a pulse signal,but also based on a DC level of the pulse signal, so to provide a morerobust detection of the timing control information when compared toprior art implementations using non-galvanic coupling discussed above.This can allow regeneration of the timing control signal even in caseswhere an edge is not detected, due for example, to a switching eventoccurring during a detection phase of the edge, as the level of thepulse signal will be detected after the switching event. As described inthe following paragraphs of the present disclosure, a coupling to thelevel shifter, according to various embodiments of the presentdisclosure can allow transmission of both edge information and DC levelinformation of a pulse signal representative of the timing controlinformation to the level shifter.

In addition, by implementing a single chip silicon on insulator (SOI)MOSFET solution based on low voltage MOSFETs, additional functionalitycan be included which addresses additional areas known to a person ofordinary skill in the art such as, but not limited to, GaN gate voltageoverdrive protection, minimum gate drive requirements, dead timecontrol, temperature stability, floating node tracking and startupvoltage condition among others.

The present disclosure describes a level shifter circuit capable ofdriving control voltages or analog signals at relatively low voltagessuch as about 0 volts to 3.5/5 volts, while riding, or “flying,” on topof high voltages substantially higher than the low voltages, such as12-100 volts or higher. The level shifter according to the presentdisclosure uses low breakdown voltage transistors that operate withrespect to a flying reference voltage (12-100 volts or higher).

The level shifter according to the present disclosure uses a parallelresistive-capacitive coupling to receive timing control information froma low voltage circuit operating with respect to a fixed referencevoltage. The parallel resistive-capacitive coupling allows transmissionof edge information and DC level information of a pulse signalrepresentative of the timing control information from the low voltagecircuit to the flying reference voltage. By receiving edge and DC levelinformation, the level shifter according to the present disclosure canregenerate the pulse signal in its entirety and therefore control thehigh voltage semiconductor devices in a more robust and efficientmanner. In particular, operation of the level shifter according to thepresent disclosure can be immune to a missed (undetected) edge of thepulse signal as control of the high voltage semiconductor devices incase of such missed edge may be provided based on DC level informationof the pulse signal received by level shifter through the parallelresistive-capacitive coupling. This allows control of the high voltagesemiconductor devices without missing a cycle (e.g. representative ofON/OFF states of the high voltage devices) for an increased protectionand more efficient operation of the high voltage devices.

The various embodiments presented herein describe low voltage control ofhigh voltages performed by the novel level shifter which enables propercontrol of high voltage devices using low (breakdown) voltagetransistors of the level shifter, where the low breakdown voltage issubstantially smaller than the high voltage, and where the control isbased on edge information and DC level information of a pulse signaltransmitted to the level shifter through the parallelresistive-capacitive coupling.

As used in the present disclosure, a high voltage device or high voltagetransistor refers to a semiconductor transistor device which canwithstand and block (e.g. in the OFF state) DC voltages (typicallyapplied between the source and drain terminals of the transistor, or anytwo of drain, source and gate terminals) greater than 5-10 volts, andmore typically substantially greater than 5-10 volts, such as greaterthan 12-100 volts. Some exemplary high voltage devices are depletionmode GaN transistors (d-GaN), enhancement mode GaN transistors (e-GaN),stacked MOS transistors, and other high-voltage transistors known to aperson skilled in the art, such as Si MOSFETs, hexagonal shape FETs(HEXFETs), LDMOS, indium phosphide (InP), etc. which can also beenhancement or depletion modes (e.g. e-type or d-type) and N or Ppolarity.

In the present disclosure e-GaN FET transistors are used as exemplaryhigh voltage devices in order to describe the various embodiments of thepresent application, and therefore such exemplary usage should not beconstrued as limiting the scope of the invention as disclosed herewith.Unless explicitly mentioned as d-GaN, the terms GaN and e-GaN areconsidered synonymous herein.

A person skilled in the art can recognize that depletion mode d-GaNdevices or other types of high voltage transistors such as Si MOSFETs,HEXFETs, LDMOS, InP (and all these examples can be of the e-type ord-type; and N or P polarity) or virtually any device capable ofswitching ON or OFF with high voltages applied can be controlled usingthe parallel resistive-capacitive coupling in accordance with theteachings of the present disclosure. A person skilled in the art wouldknow that specific design considerations in view of a desire to controla specific type of a high voltage transistor may also be needed,description of which is beyond the scope of the present disclosure.

E-GaN devices have typical threshold, or turn-on, voltages ofapproximately +0.7 to +3 volts of gate-to-source voltage. Such devicesare typically capable of withstanding 5 to 200 volts of drain-to-source,V_(DS), voltage, thereby enabling high voltage applications, such as,for example, DC/DC power conversion from a high input voltage to a lowoutput voltage. GaN transistors are used in the present disclosure as anexemplary approach to high voltage power management due to the knownadvantageous characteristics of GaN transistors, such as, for example, alow FOM.

Throughout this description, embodiments and variations of the levelshifter are described for the purpose of illustrating uses andimplementations of the inventive concept. The illustrative descriptionshould be understood as presenting examples of the inventive concept,rather than as limiting the scope of the concept as disclosed herein.

The various embodiments of the present disclosure can be used inapplications where efficient and robust control of high voltage devicesis desirable using low voltage transistors. Although the exemplary caseof DC/DC converters is used to describe the various embodiments of thelevel shifter according to the present disclosure, such exemplary caseshould not be construed as limiting the scope of the invention asdisclosed herewith. The person skilled in the art is able to use theteachings according to the present disclosure and apply such teachingsto specific applications where low voltage control of high voltages isdesired. One example of other category of possible applications is inthe area of class-D audio amplifiers.

FIG. 1 shows two stacked GaN transistors, T1 and T2, which can be usedas a basis for high voltage stacked GaN transistors. As used in thepresent disclosure, transistors T1 and T2 can be referred to as,respectively, the low side (LS) transistor and the high side (HS)transistor, and any controlling element associated in controlling the LStransistor and the HS transistor can likewise be referred to as,respectively, the low side (LS) control and the high side (HS) control.In the present disclosure, DC/DC conversion serves as an exemplaryapplication for control of stacked high voltage transistors whoseteachings can be applied to other applications where stacked transistorscontrol voltages larger than the inherent voltage handling capability ofconventional control devices (e.g. using low voltage controltransistors). A person skilled in the art will recognize that while theexemplary DC/DC converter using the stacked transistor of FIG. 1 relieson two stacked GaN FETs T1 and T2, the inventive control systemdisclosed herein can be applied to a stack height of one, as well as tolarger stack heights of three, four, or any number of stackedtransistors, and to any high voltage transistor made in other materialsand/or fabrication processes.

FIG. 2 shows a prior art embodiment of a gate driver circuit (210) usedfor controlling the stacked GaN transistors T1, T2 of FIG. 1 using(exclusively) low (breakdown) voltage transistors. Such prior artcircuit depicted in FIG. 2 can be used for implementing, for example, aDC/DC converter. The input voltage, V_(IN), shown in FIGS. 1 and 2,applied to the drain of the top transistor T2 (high side transistor) ofthe stack can be as high as the voltage handling capability of thechosen GaN transistors T1 and T2 (e.g. 12 volts-100 volts or higher). Asknown by a person skilled in the art, based on the input voltage V_(IN),a lower voltage can be generated by controlling the length of time ofthe ON/OFF states of the two transistors. Such low voltage can beobtained, for example, by filtering a voltage at the common output nodeSW of the two transistors T1 and T2.

As can be seen in the prior art embodiment of FIG. 2, the source of thelower GaN transistor T1 is tied to a reference ground, GND, and thesource of the upper GaN transistor T2 is tied to the drain of T1, whichtogether create an output node SW.

The exemplary prior art circuit shown in FIG. 2 uses low (breakdown)voltage transistors to convert the high input voltage V_(IN), to a lowervoltage obtained via the output node SW. In one exemplary embodimentV_(IN) can be 100 volts and the lower voltage obtained via node SW (e.g.via filtering of voltage at node SW) can be about 0 volts (e.g. 100 mV).In addition to being able to handle high voltage, it is important forthe DC/DC converter of FIG. 2 to exhibit high efficiency in making sucha conversion and also doing so at a high frequency. The person skilledin the art readily understands the concept of efficiency in a powerconversion application, as well as the desired high frequency conversionwhich enables use of smaller inductive components in a filter (not shownin FIG. 2) associated to the output node SW. GaN devices provide highefficiency due to their low Ron, as discussed above, whilesimultaneously switching at high speed due to their low Cg.

By using low voltage transistors throughout the control circuitry, suchas, for example, MOSFETs, low cost, high precision and high volume CMOSmanufacturing techniques can provide the necessary control circuit (e.g.gate driver 210 of FIG. 2) while keeping the performance advantagesprovided by the high voltage GaN FET transistors (T1, T2), therebyeliminating the need for more exotic, high voltage transistors in thecontrol circuit. Such low voltage MOSFETs (e.g. SOI MOSFETs) in thecontrol circuit can also enable single chip embodiments where additionalcontrol or signal processing capabilities can be integrated within asame monolithically integrated chip. The person skilled in art canappreciate such integration, as single chip devices (e.g. monolithicintegration) typically offer the most reproducible, reliable and lowestcost solutions possible in the electronics arts.

The gate driver circuit (210) of the prior art embodiment depicted inFIG. 2 controls the switching of the LS transistor and the HS transistorof the high voltage stacked transistors depicted in FIG. 1 between theirrespective ON and OFF states to provide a desired voltage, based on theinput voltage V_(IN), at node SW. The gate driver circuit (210) controlsthe switching of the LS transistor T1 and the HS transistor T2 byproviding the gate voltages needed to turn ON or OFF each of the twotransistors T1 and T2, typically in an alternating fashion, where onlyone of the two transistors can be ON (or OFF) at any one time. Such gatevoltages can be obtained via a feedback loop (not shown) between afiltered voltage based on the voltage at node SW and the input terminalIN to the gate driver circuit (210). The person skilled in the artreadily knows that a pulse width modulator (PWM) controlled by thefiltered voltage (e.g. at node SW) can be used in such feedback loop toprovide low voltage control timing pulses to the gate driver circuit(210). Such low voltage timing pulses can be fed to the common inputlogic block (215) of the driver circuit (210) of FIG. 2, andsubsequently conditioned and fed to the HS level shifter (225) and theLS control block (235), both including low (breakdown) voltagetransistors.

With continued reference to FIG. 2, the HS level shifter (225) convertsthe low voltage timing pulses to a voltage level adequate to control thegate-to-source voltage of the HS transistor T2 of the high voltagestacked transistors of FIG. 1 even as its source node, SW, rises andfalls between V_(IN) and GND. As can be seen in FIG. 2, coupling betweenthe input logic block (215) operating with respect to a fixed referencevoltage (e.g. GND) and the HS level shifter operating with respect to aflying reference voltage (SW) is achieved by way of a capacitivecoupling (220). The HS control circuit (225, 255) operates with respectto a flying reference voltage that is the switching voltage (SW) at theoutput node of the DC/DC converter depicted in FIG. 2.

In a typical implementation and upon a power up sequence, the gatedriver circuit (210) of the prior art embodiment depicted in FIG. 2 caninitially turn off either the high side transistor (T2) or both the highside and the low side transistors (T1, T2) to ensure that both T1 and T2are in a safe OFF state while all other DC/DC converter associatedcircuitry stabilizes upon the power-up. Subsequently, the gate driver(210) can control a DC voltage conversion (e.g. V_(IN) to SW) byinitially turning on the low side (LS) transistor T1 by driving its gatevoltage above its threshold voltage while turning OFF the high side (HS)transistor T2. This brings the voltage at node SW to GND since T1 isconducting and therefore its V_(D)S can be very close to zero. Also,since the source of T2 is close to GND, the HS transistor T2 holds offall of the V_(IN) voltage applied to its drain (e.g. its V_(DS)=V_(IN)).

Alternatively, when the gate driver (210) of the prior art embodimentdepicted in FIG. 2 turns OFF LS transistor T1 and turns ON the HStransistor T2 of FIG. 2, the output node SW is charged high toward thevoltage V_(IN). Since the HS transistor T2 is conducting and the LStransistor T1 is not conducting, during the ON period (e.g. length oftime of ON state) of the HS transistor T2, the output node SW will havea nominal voltage equal to V_(IN), other than during a correspondingcharging and discharging period at the beginning and end of the ONperiod. During the ON period of T2, the gate voltage of HS transistor T2stays positive (e.g. by a voltage equal to Vdd2 as provided by theVdd2+SW supply to the HS transistor T2 controlling blocks (225, 255))with respect to the voltage at the output node SW such as to keep the HStransistor T2 ON and conducting strongly (e.g. Vdd2≥V_(th) of T2, whereVth is the threshold voltage of HS transistor T2), thereby keeping thevoltage at node SW at V_(IN). A person skilled in the art will recognizethat the capacitive coupling (220) drops the V_(IN) high voltage whichcan therefore avoid impressing of such high voltage upon the low voltagetransistors of the HS control circuits (225, 255) of the gate driver(210) depicted in FIG. 2.

As discussed above, the capacitive coupling (220) to the HS levelshifter (225) depicted in FIG. 2 only allows transmission of edgeinformation of a pulse signal HX representative of the timing controlinformation provided at the input terminal IN of the gate driver circuit(210). FIG. 3A shows a timing diagram representative of a processing ofthe pulse signal HX where a leading edge LE and a trailing edge TE ofthe pulse signal HX are shown. An edge detection circuit within the HSlevel shifter (225) detects the LE and TE edges and generates acorresponding signal, Detected Edges signal. The Detected Edges signalis passed to a processing circuit that generates therefrom a gatecontrol pulse, T2 Gate Control, at a voltage appropriate to controlON/OFF state of the HS transistor T2. Due to delays in the processingcircuit, the generated T2 Gate Control signal may have edges that aredelayed with respect to edges of the Detected Edges signal as shown inFIG. 3A, where the processing delay, LE Processing Delay, of thedetected LE edge is shown.

As shown in FIG. 3B, the edge detection circuit typically includes aresistor R_(TOP) that is in series connection with the capacitivecoupling (220) at the input. The resistor R_(TOP) is used to set a DCvoltage bias level (Bias Voltage) at an input of the edge detectioncircuit that follows. The capacitive coupling (220) and the resistorR_(TOP), therefore establish a change of voltage level based on areceived edge of the pulse signal (e.g. HX) as shown in FIG. 3B. Thesubsequent edge detection circuit then converts the edge informationinto logic and timing information to control the HS transistor T2. Dueto a delay within the processing circuit, the leading edge LE of thegate control pulse may be delayed by an amount close to a pulse durationof the pulse signal HX, and therefore a high voltage switching event atthe node SW may occur concurrently with an edge detection of thetrailing edge TE of the pulse signal HX. Such concurrency of the highvoltage switching event with the detection of the trailing edge TE mayin turn negatively affect the detection circuit in a way to cause thetrailing edge TE not being detected, and therefore potentially corruptthe gate control pulse that controls the HS transistor T2. Suchcorruption may induce a lengthened ON state of the HS transistor T2 thatoverlaps an ON state of the LS transistor T1 thereby causing shootthrough currents though the stacked transistors T1, T2. A person skilledin the art is well aware of ill effects associated to the shoot throughcurrent, such as, for example, reduction in efficiency of the DCconverter, potential risk of damage to the transistors (T1, T2) beingdriven, and potential risk of damage to a power supply generating theV_(IN) voltage due to increased stress.

Although the timing diagram depicted in FIG. 3A shows a potential edgedetection issue with respect to a trailing edge (TE) of the pulse signalHX, a person skilled in the art would realize that same issue may bepresent in detection of either the trailing or leading edges of thepulse signal HX with similar ill effects as described above.

As shown in the timing diagram of FIG. 3C, edge detection issues mayalso arise when the node SW switches from a low voltage to a highvoltage immediately after the LS transistor T1 is switched OFF. In thiscase, a negative inductor current induced by an inductor, part of afilter coupled to the SW node, drives the voltage at the node SW towardsthe high voltage, causing a switching event. Assuming a dead-time thatseparates the ON state of the HS transistor T2 and the ON state of LStransistor T1 is roughly equal to the edge processing delay of theleading edge LE of the HX signal, then detection of the LE edge of theHX signal may occur concurrently with the switching event. It should benoted that the timing diagrams depicted in FIGS. 3A and 3C are merely tohelp understand possible edge detection issues in the capacitivelycoupled HS level shifter of the prior art in view of vicinity of aswitching event to an edge detection event without necessarily showingto scale signal levels and timings, including rising and falling slopesof the depicted signals.

Based on the above potential issues with the prior art capacitivelycoupled HS level shifter, mainly due to being limited to receive onlyedge information of a pulse signal representative of timing controlinformation, embodiments according to the present disclosure provide anHS level shifter capable of receiving and processing edge information aswell as DC level information of the pulse signal. This allowsregeneration of the pulse signal in the high voltage domain within whichthe HS level shifter operates in spite of a missed edge. If a switchingevent is concurrent with an edge detection phase in a way to cause amissed edge, the HS level shifter according to the present disclosurecan respond to the DC level information and generate an appropriate HSgate control signal, therefore maintaining proper functionality of theDC/DC converter.

FIG. 4 shows a block diagram of a gate driver circuit (410) according toan embodiment of the present disclosure which can be used to control theLS transistor T1 and the HS transistor T2 of the high voltage stackedGaN transistors of FIG. 1. In contrast to the prior art gate drivercircuit (210) of FIG. 2 where a capacitive coupling (220) is used totransmit edge information to the HS level shifter (225) and drop thehigh voltage V_(IN), the gate driver (410) according to the presentdisclosure uses a parallel resistive-capacitive coupling to transmitboth edge and DC level information the HS level shifter (425) whiledropping the high voltage V_(IN).

As can be seen in FIG. 4, pulse signal HX, representative of the timingcontrol information provided at the input terminal IN of the gate drivercircuit (410) and generated by the common input logic block (215)operating in the first (static) voltage domain (GND, Vdd1), istransmitted, through the parallel resistive-capacitive coupling (420),to the HS level shifter (425) operating in the second (flying) voltagedomain (SW, Vdd2+SW). The gate driver circuit (410) according to thepresent disclosure, via its HS control circuit (420, 425, 455) and LScontrol circuit (435), therefore maintains advantages provided by usingexclusively low voltage transistors while eliminating potential issuesassociated with the prior art capacitive coupling configurationdiscussed above with respect to FIG. 2. As used in the presentdisclosure, a “parallel resistive-capacitive” coupling or network, suchas, for example, the parallel resistive-capacitive coupling (420) ofFIGS. 4, 5A, 5C, 6A, 6B, 7, and 9A, the parallel resistive-capacitivenetwork (R_(TOP), C_(TOP)) of FIGS. 6A, 6B, 7, and 9A, and the parallelresistive-capacitive network (R_(BIAS), C_(BIAS)) of FIGS. 6A, 6B, 7,and 9A, according to the present teachings comprises at least oneparallel resistor-capacitor network that comprises a network of one ormore series connected resistors in a parallel connection with a networkof one or more series connected capacitors. The network of one or moreseries connected resistors and the network of one or more seriesconnected capacitors may be coupled to one another via at least twocommon nodes that define the parallel connection.

As shown in FIG. 4, a pulse signal LX, which may be a complementarysignal to the HX input signal and representative of the same timingcontrol information, is provided to the LS control circuit (435) togenerate a gate control pulse at a voltage appropriate to control ON/OFFstate of the LS transistor T1. According to an embodiment of the presentdisclosure, the LS control circuit (435) may be similar (e.g. same) tothe combination circuits (425, 455) used to control the HS transistor T2so to provide a processing time delay of the LX signal through the LScontrol circuit (435) that is substantially equal to one provided to theHX signal through the HS control circuit (420, 425, 455). Furtherimplementation details of the LS control circuit (435) may therefore beomitted.

FIG. 5A shows an exemplary embodiment according to the presentdisclosure of the parallel resistive-capacitive coupling (420),comprising a resistor R20 in parallel connection with a capacitor C20which are used to transmit edge information and DC level information ofthe input pulse signal, Pulse. The fast response time of the capacitorC20 transmits accurate edge information of the pulse signal Pulse to theHS level shifter (425), while the resistor R20 provides a transmissionpath for the DC level information of the pulse signal to the HS levelshifter (425). As noted above, the capacitor C20 is used to drop thehigh voltage V_(IN) and therefore allows safe operation of the lowvoltage transistors of the HS level shifter (425). In addition, theresistor R20 drops the high voltage Vin and therefore also allows safeoperation of the low voltage transistors of the HS level shifter, 425.

The parallel resistive-capacitive coupling (420) is complemented by aparallel resistive-capacitive network comprising a resistor R_(TOP) anda capacitor C_(TOP) that are also connected in parallel, having a firstcommon node coupled to the flying supply Vdd2+SW and a second commonnode coupled to a common node of the resistive capacitive coupling (420)where a detected pulse is provided.

With continued reference to the parallel resistive-capacitive couplingaccording to the present disclosure depicted in FIG. 5A, a personskilled in the art would realize that the coupling between the parallelresistive-capacitive coupling (420) and the parallelresistive-capacitive network (R_(TOP), C_(TOP)) forms a capacitivevoltage divider (C20, C_(TOP)) that establishes a transient (dynamic)voltage response for generation of edges of the detected pulse, and aresistive voltage divider (R20, R_(TOP)) that establishes a staticvoltage response for generation a DC level of the detected pulse.According to an embodiment of the present disclosure a capacitance ratioof C_(TOP)/C20 can be inversely proportional, or approximately inverselyproportional, to a resistance ratio of R_(TOP)/R20 so that to provide asmooth transition between the transient and the static responses,thereby generating a detected pulse similar in shape to the input pulse(as shown in FIG. 5B) with a reduced amplitude (difference between lowand high voltage levels).

A person skilled in the art would realize that monolithic integration ofthe gate driver (410) of FIG. 4, including the parallelresistive-capacitive coupling (420), may set limits on a withstandvoltage of the capacitor C20. It may therefore be desirable to replacethe single capacitor (C20) with a plurality of series connectedcapacitors so as to allow a higher combined withstand voltage in anintegrated configuration, as shown in FIG. 5C. In the configurationdepicted in FIG. 5C, total capacitance of the series connectedcapacitors (C20 ₁, C20 ₂, . . . , C20 _(n)) can be made according to thevalue of the capacitor C20 described above with reference to FIG. 5A.Also, the total resistance of the series connected resistors (R20 ₁, R20₂, . . . , R20 _(n)) can be made according to the value of the resistorR20. A person skilled in the art would realize that other parallelresistive-capacitive coupling configurations based on the configurationsdepicted in FIG. 5A and FIG. 5B are also possible, where a capacitivecoupling is used to establish a transient voltage response to regenerateedges of a detected pulse and a resistive coupling is used to establisha static voltage response to regenerate a DC level of the detectedpulse. As used herein, “equivalent capacitance” of the parallelresistive-capacitive coupling (420) refers to the total capacitance ofthe series connected capacitors (C20 ₁, C20 ₂, . . . , C20 _(n)) and maybe represented by a single capacitor C20 having the equivalentcapacitance, as depicted in FIG. 5A.

With further reference to FIG. 5C, it should be noted that althoughnumbers of the series elements of R20 _(i) and C20 _(i) may be differentand yet provide a functionally working configuration. However, in someembodiments, for robustness and reliability concerns, “floating”intermediate nodes of the series connected capacitors C20 _(i) may notbe desired. If there is a capacitive node that is not connected to aresistor, the DC voltage at such capacitive node would be dependent on avery small and highly variable leakage current of an associatedcapacitor. Such leakage current may in turn contribute to mismatchedvoltage drops across the capacitors C20 _(i) where, for example, onecapacitor may have a large drop and another capacitor may have a smallerdrop. The voltage rating of the capacitor should therefore be consideredin view of the large drop in voltage.

With continued reference to FIG. 5C, a person skilled in the art wouldunderstand that since the capacitor C20 drops the voltage V_(IN), or avoltage substantially equal to V_(IN), the capacitance ratio C_(TOP)/C20should be large enough, and therefore the resistance ratio R20/R_(TOP)should also be large enough to keep the absolute voltage of the detectedpulse, Detected Pulse, between the flying voltage domain (SW, Vdd2+SW)under all operating conditions. For example, with reference to FIG. 5A,if SW node switches from 0 volts to 100 volts, and Vdd2 is equal to 5volts, then the capacitance ratio C_(TOP)/C20 should be greater than105/5=21. The following Table A shows the amplitude (voltage) of thedetected pulse signal, Detected Pulse, for a case where the capacitanceratio C_(TOP)/C20 is equal to 21, SW node switches from 0 volts to 100volts, and Vdd2 is equal to 5 volts.

TABLE A Input Pulse voltage SW node voltage Detected Pulse voltage 0volts 0 volts 4.762 volts 5 volts 0 volts 5 volts 0 volts 100 volts 100volts 5 volts 100 volts 100.238 volts

The HS level shifter according to the present disclosure is able toaccurately process low amplitude pulse signals while operating withinthe flying voltage domain (SW, Vdd2+SW). As shown in the tablerepresenting the above example, the absolute voltage of the DetectedPulse is exactly kept between the flying voltage domain (SW and Vdd2+SW)with no margin. In practice, some voltage headroom is needed away fromthe supply rails which means that the actual C_(TOP)/C20 ratio would belarger than 21 in order to bring the Detected Pulse voltage higher than100 volts when SW is at 100 volts. An additional bias circuit may beneeded to bring the Detected Pulse voltage lower than 5 volts when SW isat 0 volts which will be described later. Another advantage of the HSlevel shifter according to the present disclosure is its ability toaccurately process the low amplitude pulse signals in presence of highslew rates of the flying reference voltage SW, which according to anexemplary case can switch from 0 volts to 100 volts.

FIG. 6A shows an embodiment according to the present disclosure of a HSlevel shifter (425) with the parallel resistive-capacitive coupling(420) described above, where a flying comparator, COMP, comprisingexclusively low voltage transistors, is used to accurately process thelow amplitude pulse signals regenerated through the combination of theparallel resistive-capacitive coupling (420) and associated parallelresistive-capacitive network (R_(TOP), C_(TOP)). As used herein, theexpression “flying comparator” refers to a comparator operating in aflying voltage domain, such as the flying voltage domain defined byswitching voltages (SW, Vdd2+SW), where SW can switch from 0 volts to100 volts, and vice versa, and comprising exclusively low breakdownvoltage transistors. A person skilled in the art would appreciatebenefits provided by such flying comparator which can allow addedprecision (e.g. timing) and flexibility (e.g. wide range of output dutycycle with short length pulses) in the control of the high voltagesemiconductor devices (T1, T2). Further implementation details of theflying comparator, COMP, according to the present disclosure is providedin the following paragraphs.

According to an embodiment of the present disclosure, the flyingcomparator COMP can be provided with a differential signal obtained bytransmitting complementary input pulses (IN_A, IN_B) through respectiveparallel resistive-capacitive couplings (420), as depicted in FIG. 6A.The complementary input pulses (IN_A, IN_B) may be obtained viaprocessing of the input signal provided at the input terminal IN of thegate driver (410) depicted in FIG. 4, in which case the input signalHX=(IN_A, IN_B). Alternatively, the input signal HX may be a singlesignal and generation of the complementary input pulses (IN_A, IN_B) maybe provided within a separate circuit (not shown). The flying comparatorCOMP outputs complementary output signals (OUT_A, OUT_B) with amplitudelevels large enough for subsequent processing by low break downtransistors based logic gates (428) of the HS level shifter (425).

As can be seen in FIG. 6A, each of the input pulses (IN_A, IN_B) istransmitted through a respective parallel resistive-capacitive coupling(420) which is coupled to a respective parallel resistive-capacitivenetwork (R_(TOP), C_(TOP)). Therefore, each such input pulse issubjected to a same processing as described in relation to FIGS. 5A, 5B,5C discussed above. As can be seen in FIG. 6A, common nodes between eachparallel resistive-capacitive coupling (420) and the respective parallelresistive-capacitive network (R_(TOP), C_(TOP)) are connected to thepositive/negative inputs (also referred to as non-inverting/invertinginputs) of the flying comparator COMP. It should be noted that the inputpulses (IN_A, IN_B) being generated in the static voltage domain (GND,Vdd1) may operate between a low voltage level (e.g. 0 volts) and a high(rail) voltage level (e.g. Vdd1). According to one exemplary embodimentVdd1 can be in a range of 2.5 volts to 5 volts. According to anexemplary embodiment, Vdd2 can be in a range of 2.5 volts to 5 volts andthe switching voltage at node SW can switch between 0 volts to 100volts. It should be noted that such exemplary voltages should not beconsidered as limiting the scope of the present disclosure, as a personskilled in the art would know how to select different voltages based onestablished design goals and parameters. For example, the switchingvoltage at node SW may be switching to any high voltage that is greaterthan 12 volts, and equivalent capacitance C20 of a correspondingparallel resistive-capacitive coupling (420) may be adjustedaccordingly, if necessary.

A person skilled in the art readily knows that an input stage of acomparator, such as the flying comparator COMP of FIG. 6A, may operateover a certain range of common mode voltage of its differential inputsignal. A person skilled in the art readily knows that the common modevoltage is the DC voltage level of an input signal to the comparatorrelative to the reference voltage (e.g. voltage at node SW). Therefore,for proper operation of the flying comparator COMP, the common modevoltage of the differential input to the flying comparator COMP, asprovided by the common nodes between the parallel resistive-capacitivecoupling (420) and the parallel resistive-capacitive network (R_(TOP),C_(TOP)), should remain within an acceptable operational voltage rangeof the flying comparator COMP irrespective of a switching level of theflying voltage domain (SW, Vdd2+SW).

It follows that according to an embodiment of the present disclosure,the capacitance ratio C_(TOP)/C20 and the resistance ratio R_(TOP)/R20are configured to provide detected pulses, based on the input pulses(IN_A, IN_B), to the positive/negative inputs of the flying comparatorCOMP, with voltage levels that are within the acceptable operationalvoltage range of the flying comparator COMP. As ratios also affect theamplitude of the differential input signal to the flying comparator,according to some exemplary embodiments of the present disclosure, suchratios may be configured to provide common mode voltage levels of theinput differential signal that are within the acceptable operationalvoltage range of the flying comparator while providing as large anamplitude of the differential input signal to the flying comparator aspossible. A person skilled in the art would recognize that selecting theratios based on the high voltage level of the flying voltage domain (SW,Vdd2+SW), e.g. (100 volts, 105 volts), would satisfy conditions for boththe common mode voltage range and the differential signal amplitude forthe low voltage level of the flying voltage domain (e.g. 0 volts, 5volts). Capacitances of Crop and C20 may also be adjusted in view of anyparasitic capacitance that may be present in a final layout of the levelshifter according to the present teachings. In this case, and as notedabove, ratios C_(TOP)/C20 and R_(TOP)/R20 may be chosen to beapproximately inversely proportional in view of the parasiticcapacitance. It should be noted that such inverse proportionalityrelationship need not be exact, but rather considered as anapproximation.

A person skilled in the art would also realize that selecting the ratiosfor a given high voltage level of the flying voltage domain (SW,Vdd2+SW), of for example, (100 volts, 105 volts), such as to providecommon mode voltage levels of the input differential signal that arewithin the acceptable operational voltage range of the flying comparatorCOMP, such selected ratios would also satisfy operational voltage rangerequirements of the flying comparator for lower high voltage levels,such as, for example, (50 volts, 55 volts). In such cases where lowerhigh voltage levels are provided, it may be desirable, but notnecessary, to increase the amplitude of the differential input signal tothe flying comparator. According to an embodiment of the presentdisclosure, such increased amplitude of the differential input signalmay be provided by way of charge pump circuits (215 a, 215 b) thatincrease the voltage level of the complementary input pulses (IN_A,IN_B) as depicted in FIG. 6B.

The programmable charge pump circuits (215 a, 215 b) may also be used toprogrammatically adjust voltage levels of the complementary inputs(IN_A, IN_B) according to different values of the high voltage level ofthe flying voltage domain (SW, Vdd2+SW). This can allow operation athigher high voltage levels (e.g. 200-300 volts and above) bycompensating a reduction in amplitude of the differential input signalto the flying comparator, due to a required higher capacitance ratioC_(TOP)/C20, with an increase in amplitude of the input pulses (IN_A,IN_B), thereby effectively providing an amplitude of the differentialinput signal at a level that is detectable by the flying comparatorCOMP. It should be noted that although FIG. 6B shows the charge pumpcircuits (215 a, 215 b) as part of the common input logic block (215),such exemplary partitioning should not be considered as limiting thescope of the present disclosure, as a person skilled in the art wouldrealize that the charge pumps (215 a, 215 b) may also be part of the HScontrol circuit (420, 425, 455) as shown in FIG. 6C. In general, aperson skilled in the art would know how to partition the circuitsdiscussed in the present application based on specific applications andpackaging. As such, partitioning shown in the various figures of thepresent disclosure should not be considered as limiting the scope of thepresent disclosure.

With further reference to the HS level shifter (425) according to thepresent disclosure depicted in FIG. 6A, biasing points (e.g. voltages)of an input stage of the flying comparator COMP are provided by aparallel resistive-capacitive network (R_(BIAS), C_(BIAS)) coupled tothe positive/negative inputs of the flying comparator COMP. The fastresponse time of the capacitor C_(BIAS) allows quick tracking of thebiasing points responsive to a flying event of the flying voltage domain(SW, Vdd2+SW), while the resistor R_(BIAS) allows for maintaining thebiasing points based on settled voltage levels of the flying voltagedomain (SW, Vdd2+SW). A person skilled in the art would realize thatsuch biasing points establish voltage levels at the positive/negativeinputs of the flying comparator COMP that remain within the operationalvoltage range of the flying comparator COMP discussed above.

Further details of the HS level shifter (425) according to the presentdisclosure are shown in FIG. 7. In particular, FIG. 7 depicts innercircuit blocks of the flying comparator COMP which are well known to aperson skilled in the art. As can be seen in FIG. 7, such inner circuitblocks may include an Input Stage and an Output Stage. The Input Stagecomprises transistors (M1, M2, M3) and a Load circuit for providing aload (e.g. passive, active) to the differential input signal, and iscoupled to the positive/negative input terminals (denoted +, − in FIG.7) of the comparator COMP for receiving the differential input signal(e.g. via transistors M1, M2). The Output Stage is shown as an OutputStage A comprising transistors (M4, M6) and an Output Stage B comprisingtransistors (M7, M8), the Output Stage A and Output Stage B coupled torespective output terminals of the comparator COMP for outputting thecomplementary output signals (OUT_A, OUT_B) via transistors (M4, M7).Other transistors, such as transistors (M3, M5, M6, M8) may be used, forexample, to provide current biasing to the various inner circuit blocks(e.g. to the Input Stage and the Output Stage). It should be noted thatinner workings of a comparator are well known to a person skilled in theart and outside the scope of the present disclosure.

With further reference to FIG. 7, as noted above, the varioustransistors (e.g. M1-M7) used in the inner circuit blocks of the flyingcomparator according to the present disclosure are exclusively lowvoltage transistors, capable of withstanding, for example, the lowvoltage Vdd2 (e.g. 2.5 volts to 5 volts). A person skilled in the artreadily knows that an analog comparator, such as the flying comparatorCOMP, includes current biasing circuits that produce conditions wherelow voltage transistors of the flying comparator COMP may have highimpedance nodes (e.g. gate, drain, source) with respect to the supplyvoltage. Some such transistors may also have nodes with low impedancewith respect to the supply voltage.

Therefore, and with reference to FIG. 8A, in a case where the supplyvoltage flies (switches) from a first voltage (e.g. Vdd2=5 volts) to asecond voltage (e.g. Vdd2+SW=105 volts) in a time (e.g. 1 ns) shorterthan a voltage response time of a high impedance node of a low voltagetransistor M81, voltage at the high impedance node would lag the voltageat a low impedance node (having a fast voltage response time obtained,for example, via a capacitive coupling to the flying voltage). The lagin voltage between the two nodes can therefore create a voltage dropacross the two nodes of the transistor that is substantially larger thana withstand (e.g. breakdown) voltage of the transistor, thereby causinggate breakdown (TDDB) or hot-carrier injection (HCI) related reliabilityissues of the transistor M81. It follows that according to an embodimentof the present disclosure, clamps comprising exclusively low voltagetransistors are strategically used across such low impedance and highimpedance nodes of devices within the flying comparator COMP of thepresent disclosure, thereby allowing safe operation of the low voltagedevices in spite of a high slew rate of the flying supply. This is shownin FIG. 8B. Such clamps may be coupled to either a top local supply rail(e.g. Vdd2+SW), referred to as top clamps, or a bottom local supply rail(e.g. SW), referred to as bottom clamps.

With reference to FIG. 8B, a low voltage transistor M82 functions as aclamp according to the present disclosure to pull the high impedancenode of the low voltage transistor M81 to the flying voltage (Vdd2+SW)when a voltage difference between the high impedance node and the lowimpedance node of the transistor M81 becomes sufficiently low ornegative (while remaining within a withstand voltage of the transistor)to trigger the clamping transistor M82. It should be noted that the lowvoltage transistor M81 can be any low voltage transistor within theflying comparator COMP having combination of high impedance and lowimpedance nodes with respect to the flying voltage. In other words,clamping according to the present disclosure can be provided to nodesother than nodes associated with the input stage of the flyingcomparator shown in FIG. 7. A person skilled in the art would appreciatethe benefits of using low voltage transistors (e.g. M82) for providing aclamping feature according to the present disclosure, and therefore notrequiring high voltage devices, such as, for example, high voltagerectifiers as known in the art. It should also be noted that the lowimpedance node of the transistor M81, which has a gate capacitance Cg,may only be considered as low impedance during a fast transition of theswitching voltage SW. Also, the high impedance node of the transistorM81 may be considered as high impedance only when the voltage at thatnode decreases to turn OFF the transistor M81 (e.g. Vgs>Vth), otherwise,such node is a low impedance node (e.g. Vgs<Vth).

According to some exemplary embodiments, the low voltage Vdd2 of theflying voltage domain (SW, Vdd2+SW) may be greater than a voltagewithstand capability of the low voltage transistors used in the HS levelshifter (425) according to the present teachings. According to anon-limiting exemplary case, the voltage withstand capability of the lowvoltage transistors may be 2.5 volts, and the voltage Vdd2 may be about5 volts. Accordingly, in order to protect the low voltage transistors ofthe flying comparator COMP and other circuits within the HS levelshifter (425), cascode transistor configurations, as known to a personskilled in the art, may be used to divide the voltage Vdd2 across morethan one low voltage transistor, so that no transistor is subjected toany voltage higher than its voltage withstand capability. This is shownin FIG. 9A, where the (differential) Input Stage of the flyingcomparator COMP comprises a (differential) Cascode Stage, comprisingtransistors (M11, M12), that further divides the voltage Vdd2 acrosstransistors of the flying comparator COMP so that no transistor issubjected to a voltage higher than its voltage withstand capability. Asshown in FIG. 9A, a separate parallel resistive-capacitive network(R_(BIAS), C_(BIAS)) may be provided for biasing transistors of theCascode Stage.

Further limiting of voltage across any two nodes of the low voltagetransistors used in the flying comparator COMP and other circuits withinthe HS level shifter (425) according to the present teachings may beprovided by biasing associated internal transistors via a mid-railflying biasing voltage VMID based on the flying voltage domain (SW,Vdd2+SW). The mid-rail flying biasing voltage VMID can be configured tobe at a voltage level ½ *Vdd2 above the flying reference voltageprovided at node SW. For example, in a case where the flying referencevoltage at node SW flies from 0 volts to 100 volts and Vdd2 is equal to5 volts, then the mid-rail flying biasing voltage VMID flies from 2.5volts to 102.5 volts. As shown in FIG. 9A, transistors (M13, M14, M16,M17, M18) are biased with the mid-rail flying biasing voltage VMIDprovided to the flying comparator COMP.

FIG. 9A shows the mid-rail flying biasing voltage VMID fed to gates ofinternal low voltage transistors of the flying comparator COMP such asto limit voltage drop across any two nodes of the low voltagetransistors to within associated voltage withstand capability of thetransistors (e.g. 2.5 volts), while operating the flying comparator COMPfrom the flying voltage domain (SW, Vdd2+SW), where Vdd2 is greater thansaid withstand voltage (e.g. Vdd2=5 volts). As can be seen in FIG. 9A,by biasing the output stage of the flying comparator COMP with themid-rail flying biasing voltage VMID, complementary output signals(OUT_2A, OUT_2B can be made to operate within levels SW and ½ *Vdd2.Similarly, FIG. 9B shows a logic gate (900) operating in the flyingvoltage domain (SW, Vdd2+SW) comprising low voltage transistors M91-M94having a voltage withstand capability of (½ *Vdd2), wherein the mid-railflying voltage VMID biases transistors M92, M93 such as to limit voltageacross any two nodes of the transistors M91-M94 irrespective of anoutput state condition at the output terminal OUT of the logic gate(900).

With further reference to the logic gate (900) of FIG. 9B, a personskilled in the art would realize that transistors M91, M92 may beconsidered as a logic inverter having an input IN₁ operating within theflying voltage domain (SW+½*Vdd2, SW+Vdd2) and transistors M93, M94 maybe considered as a logic inverter having an input IN₂ operating withinthe flying voltage domain (SW, SW+½*Vdd2). As can be seen in FIG. 9B,when both inputs IN₁, IN₂ are at their low states, the output state atthe OUT terminal is at a high state with a corresponding voltage levelof Vdd2+SW, and when both inputs IN₁, IN₂ are at their high states, theoutput state at the OUT terminal is at a low state with a correspondingvoltage level of SW. A person skilled in the art would recognize thatfor a combination of input logic states (IN₁, IN₂)=(High, Low), avoltage level at the OUT terminal can be at SW+½*Vdd2.

It is within the ability of a person skilled in the art to design, basedon the exemplary logic inverters of FIG. 9B discussed above, logic gateswith different functionalities (AND, NAND, NOR, OR, etc.) operating oneither (SW+½*Vdd2, SW+Vdd2) or (SW, SW+½*Vdd2) flying voltage domains,where the mid-rail flying voltage VMID is used to bias transistorshaving a voltage withstand capability that is lower than the Vdd2voltage. It follows that the logic gates (428) of the HS level shifter(425) depicted in FIG. 6A can be designed to operate on either(SW+½*Vdd2, SW+Vdd2) or (SW, SW+½*Vdd2) flying voltage domains.According to some exemplary embodiments, separate level shifters may beused to shift the logic rails. These types of level shifters thatprovide a fixed voltage shift (e.g. 0-2.5V to 2.5-5V) are known to aperson skilled in the art.

The flying comparator COMP has complementary output signals (OUT_A,OUT_B) that are high impedance. During a fast SW flying event, these twooutputs generally come together (i.e. reach a substantially same valuewhile the flying voltage domain flies). For example, if OUT_A=logic 0and OUT_B=logic 1, SW flying high (i.e. switching from 0 volts to 100volts) would cause the OUT_B logic 1 to drop to logic 0 and activate abottom clamp during the switching transient. Conversely, SW flying low(i.e. switching from 100 volts to 0 volts) would cause OUT_A logic 0 togo up to logic 1 and activate a top clamp during the switchingtransient. Effectively, OUT_A−OUT_B=0 during SW flying event, as shownin the timing diagram of FIG. 10A. This allows in turn to identify aswitching event at the switching node SW via the difference signal, andaccordingly act upon during a processing phase by the logic gates (428of FIG. 6A) of the output signal OUT. In other words, clamping of thehigh impedance nodes of the flying comparator COMP along with logiccircuit around a latch according to the present teachings creates afilter-like block that removes unwanted glitches during a switchingevent.

It follows that by designing logic that is configured to act only uponnon-zero values of the difference signal OUT_A−OUT_B (and thereforereject any zero values), an output signal OUT of the HS level shifter(425) according to the present disclosure that is immune to any effectsof switching events at the switching node SW may be provided. Suchexemplary logic circuit is shown in FIG. 10B, where an SR (set-reset)latch (130) is used to act only upon non-zero values of the differencesignal OUT_A−OUT_B. A person skilled in the art is well aware of theprinciple of operation and function of the latch (130), including itstwo stable output states selected via complementary input levels to theSR latch (130). Auxiliary logic gates, including inverter gates (110,115), NAND gates (120, 125), and AND gate (140) complement the SR latch(130) to provide a desired functionality of the logic gate circuit (428)according to the timing diagram of FIG. 10A. It should be noted that thelogic gates depicted in FIG. 10B may include exclusively low voltagetransistors having a voltage withstand capability (e.g. ½ *Vdd2) that islower than the voltage Vdd2 (e.g. 5 volts). Therefore, such logic gates,as described above with reference to FIG. 9B, may operate over one of(SW, ½ *Vdd2+SW) or (½ *Vdd2+SW, Vdd2+SW).

According to one exemplary embodiment of the present disclosure, thelogic gates depicted in FIG. 10B may operate over (SW, ½ *Vdd2+SW). Ascan be seen in the corresponding timing diagram of FIG. 10A, a trippingpoint of the logic gates for the leading edge of the OUT signal occursat a mid-voltage between 0 volts and 2.5 volts (e.g. 1.25 volts) of thedifference signal OUT_A−OUT_B, and a tripping point of the logic gatesfor the trailing edge of the OUT signal occurs at a mid-voltage between−2.5 volts and 0 volts (e.g. −1.25 volts) of the difference signalOUT_A−OUT_B. Such large hysteresis (+1.25−(−1.25)=2.5 volts) provided bysaid tripping points allow for a robust design of the logic gate circuit(428) according to the present disclosure.

It should be noted that the timing diagram of FIG. 10A may be consideredas a simplified representation of functioning of the logic circuit (428)of FIG. 10B based on the difference signal OUT_A−OUT_B, which isequivalent to having roughly a 2.5 volts hysteresis to prevent thecircuit from false triggering during a flying event. For example, asshown in FIG. 10A, a −2.5 volts to +2.5 volts rising edge transition ofthe difference signal OUT_A−OUT_B may trigger the logic circuit (428) at+1.25 volts. Also, a +2.5 volts to −2.5 volts falling edge transition ofthe difference signal OUT_A−OUT_B may trigger the logic circuit (428) at−1.25 volts (providing a hysteresis of +1.25−(−1.25)=2.5 volts). On theother hand, as can be seen in FIG. 10A, any glitch due to a flying eventmay cause the difference signal OUT_A−OUT_B to go to 0 volts which isnot enough to trigger the logic used in the circuit (428). To explainhow this works, let's look at FIG. 10B. OUT_A and OUT_B arecomplementary signals. NAND gate (120) is connected to OUT_A and/OUT_B,and therefore, NAND gate (120) outputs a low logic level and set the SRlatch (130) output to high when OUT_A is high and OUT_B is low. NANDgate (125) is connected to/OUT_A and OUT_B, and therefore, NAND gate(125) outputs a low logic level to reset the SR latch (130) output tolow when OUT_A is low and OUT_B is high. Effectively, it requires twotransitions for the SR latch (130) to change state: in other words, bothOUT_A and OUT_B need to change state in order to change output state ofthe SR latch (130). As any flying event would only cause one of theoutputs OUT_A and OUT_B to change state, such flying event may not causethe SR latch (130) to change state.

According to a non-limiting embodiment of the present disclosure, theoutput signal OUT of the HS level shifter (425) may be gated by anenabling signal Enable_out, as depicted in FIG. 10B. A person skilled inthe art would realize that the logic gate circuit (428) translates adifferential input signal (OUT_A, OUT_B) to a single ended output signalOUT.

According to an exemplary embodiment of the present disclosure, theoutput signal OUT depicted in FIG. 10B may be buffered and provided tothe input IN₂ depicted in FIG. 9B. The output signal OUT may also beprovided to a level shifter that shifts its logic level from (0, ½*Vdd2) to (½ *Vdd2, Vdd2). The output of the level shifter may then beprovided to the input IN₁ depicted in FIG. 9B.

With reference back to the gate driver circuit of FIG. 4, for such DCvoltage conversion circuit to operate in an efficient and reliablemanner, it is desirable that the low side transistor T1 and the highside transistor T2 are not on at the same time, or a short circuit canexist between V_(IN) and GND (causing the shoot through current),thereby wasting power and potentially damaging the circuit and thetransistor devices T1 and T2. Due to the difference in propagation delaybetween the low side control path and the high side control path asdescribed above, often caused by layout, manufacturing or othervariations, an ON control signal (e.g. an edge of the signal output bythe LS control circuit 435) at T1 can arrive before its complementaryOFF signal (e.g. an edge of a signal output by the HS control circuit420, 425, 455) arrives at T2, therefore providing an overlap time duringwhich both transistors T1 and T1 are ON. During the overlap time, bothtransistors are ON, causing the problems noted above.

It follows that according to an embodiment of the present disclosure,the gate driver circuit (410) of FIG. 4 is fitted with a dead timecontroller to provide a dead time control as discussed above. Such deadtime controller can be part of the common input logic block (215) shownin FIG. 4, and operate between the low voltage supply Vdd1 and thereference potential GND. Therefore, the dead time controller accordingto the various embodiments of the present disclosure comprises lowvoltage transistors operating within their breakdown voltages.

FIG. 11 shows more details of a common input logic block (1015)comprising the dead time controller (1025) placed between the inputbuffer (1026) and the logic block (1027). Such common input logic blockmay be the block (215) shown in FIG. 4. As can be seen in FIG. 11, theinput signal IN is provided to the input buffer (1026) which provides abuffered version of the input signal, DT_IN, to the dead time controller(1025) for dead time adjustment. In turn, the dead time controller(1025) adjusts the edges of the DT_IN signal to provide a low side deadtime adjusted signal DT_LX and a high side dead time adjusted signalDT_HX, based on the control signals CNTL. The dead time adjusted signalsare then fed to the logic block (1027) which generates signal LX,corresponding to the signal DT_LX, to provide timing control of the lowside transistor T1, and signal HX, corresponding to the signal DT_HX, toprovide timing control of the high side transistor T2. Dead timecontroller (1025) as well as various functions of the logic block (1027)are controlled via control signals CNTL provided to the logic block(1027). According to an exemplary embodiment of the present disclosure,under control of the control signals CNTL, the logic block (1027) passesor blocks the DT_LX and DT_HX signals generated by the dead timecontroller (1025) to/from a next stage of the processing blocks of thegate driver circuit (1010) depicted in FIG. 10. The person skilled inthe art will realize that other logic functions and correspondingsignals may be required for other system level operations of the gatedriver circuit (410) of FIG. 4, which for the sake of clarity in thefunctional description of the dead time controller are not shown in FIG.4 and FIG. 11.

As seen in FIG. 11, and according to some embodiments of the presentdisclosure, the dead time control circuit (1025) produces a differentialoutput with the desired dead time based on the single ended inputsignal, DT_IN. According to the exemplary embodiment depicted in FIG.11, the dead time controller (1025) can use a fixed or programmabletiming control circuit that can generate timing adjusted signals DT_HXand DT_LX independently of one another.

As discussed above, since V_(IN) can be a large voltage, e.g. 10-100Vand higher, and an ON resistance R_(ON) of each of the GaN FETs (T1, T2)is low, e.g. <1Ω, in order not to damage transistors T1 and T2, it isdesirable that such transistors not be ON (conducting) at the same time,or equivalently, that HS_out and LS_out signals not be high at the sametime, as shown in FIG. 12A, assuming that both transistors T1 and T2turn ON at the high level of the control signals HS_out and LS_out.Having both transistors, T1 and T2, ON at the same time, leads to verylarge shoot-through currents in the transistors. This can have theundesired effect of dramatically reducing the efficiency of the circuitshown in FIG. 4, and potentially damage T1 and T2. As noted above,careful control of the timing (e.g. relative edge positions) of LS_outand HS_out signals can prevent such undesired effect. For otherapplications noted above, such as Class D audio amplifiers, having bothtransistors T1 and T2 either ON or OFF can cause signal distortion thatis a key hallmark of audio amplifiers.

FIG. 12A shows the timing relationship between the high side controlsignal, HS_out, and the low side control signal, LS_out. As discussedabove, such timing can be adjusted by the dead time control circuitaccording to the present disclosure. As can be seen in FIG. 12A, signalHS_out is high during a time interval T2 _(ON), corresponding to an ONstate of the high side transistor T2, and low during a time interval T2_(OFF), corresponding to an OFF state of the high side transistor T2.Similarly, signal LS_out is high during a time interval T1 _(ON),corresponding to an ON state of the low side transistor T1, and lowduring a time interval T1 _(OFF), corresponding to an OFF state of thelow side transistor T1.

With further reference to the timing relationship of FIG. 12A, one cansee that time intervals T2 _(ON) and T1 _(ON) are separated by non-zerotime intervals t_(DLH) and t_(DHL). Such non-zero time intervals eachdefine a positive dead time between the timing controls of the high sideand the low side transistors T2 and T1. That is, assuming that bothtransistors T1 and T2 have a same turn ON time and a same turn OFF time,their ON states will not overlap, similar to the timing diagram of theassociated control signals depicted in FIG. 12A. It should be noted thatthe dead time controller according to the present disclosure cangenerate positive and negative (described below) dead times, where thetime intervals t_(DLH) and t_(DHL) are not necessarily of a same value.

FIG. 12B shows the timing relationship between the high side controlsignal, HS_out, and the low side control signal, LS_out, for a positivedead time (i.e, t_(DLH) and t_(DHL) are both positive). According to aconvention of the present disclosure, a positive dead time is defined bya positive time interval t_(DLH) and/or a positive time intervalt_(DHL), where such time intervals are measured as the difference intiming position of a turn-ON transition (e.g. at times t₂, t₄) of acontrol signal and a turn-OFF transition (e.g. at times t₁ and t₃) ofthe alternate control signal. Accordingly, t_(DHL) is the time intervalbetween the rising transition of the low side control signal LS_out (attime t₄) and the falling transition of the high side control signalHS_out (at time t₃), therefore t_(DHL)=(t₄−t₃). Similarly, t_(DLH) isthe time interval between the rising transition of the high side controlsignal HS_out (at time t2) and the falling transition of the low sidecontrol signal LS_out (at time t₁), therefore t_(DLH)=(t₂−t₁).

Using the above convention, the timing diagram of FIG. 12B showspositive dead time for both the high side and the low side paths,whereas the timing diagram of FIG. 12C shows negative dead time for bothpaths. As stated above, positive dead time at LS_out (LS_out risingtransition comes after HS_out falling transition) and HS_out (HS_outrising transition comes after LS_out falling transition) can be apreferred condition for operating the high voltage transistors T1 andT2. In some cases where, for example, the high side and low side pathshave a fixed delay skew between them, or the transistors T1 and T2 havedifferent characteristics, it may be desirable to provide a negativedead time at one of, or both, of the LS_out and HS_out signals.Accordingly, the dead time controller according to the presentdisclosure enables both positive and negative dead times. Since theprimary usage is typically with a positive dead time, unless otherwisestated, the descriptions below should be understood to be for positivedead time.

To clarify the basic operation of the dead time controller of thepresent disclosure, it is assumed that the low side and high side pathshave equal propagation delays, which means the dead time between theDT_HX and DT_LX signals depicted in FIG. 11 (and FIG. 4) equals the deadtime between the HS_out and LS_out signals depicted in FIG. 10. For thecase of unequal propagation delays between the high side and the lowside paths, the adjusting function of the dead time control circuit ofthe present disclosure may be used to further compensate for adifference in the propagation delays.

As described above, the DC output of the overall circuit of FIG. 4obtained after filtering (e.g., by a low pass filter), is proportionalto the duty cycle at the common output node SW, hence the duty cycle ofthe high side dead time adjusted signal DT_HX is essentially equal tothe duty cycle of the input signal IN (thus of DT_IN). For the high sidesignal DT_HX to have the same duty cycle of the input signal IN, thetime intervals t_(DHSR) and t_(DHSF), as defined below in FIG. 13, areessentially equal. Again, to simplify the basic description of thecircuit while maintaining the desired DC output voltage, and therefore acorresponding desired duty cycle at the common output node SW, dead timeadjustments will be confined to the low side circuitry, while the highside circuitry will be set to follow the desired duty cycle. In otherwords, under control of the dead time controller (1025) of the gatedriver circuit (410), the high side transistor T2 is ON for a same timeduration (T2 _(ON) of FIG. 12A later described) as an ON time of anoutput of a pulse width modulator representing the average ON/OFF ratioof the signal at the common output node SW represented by the inputsignal IN to the gate drive circuit (410).

FIG. 13 shows the relative timing of the dead time controller signalsaccording to an embodiment of the present disclosure. These signalsinclude the input signal to the dead time controller, DT_IN, its highside output signal, DT_HX, and its low side output signal, DT_LX. Asstated above, to ensure the proper output DC voltage, the duty cycle, asset by the ON duration of the HS transistor T2, should equal the dutycycle of DT_IN. The timing diagram of the dead time controller depictedin FIG. 13 ensures that both transistors are not ON at the same timewhile providing a desired DC output voltage defined by the duty cycle ofthe input signal, IN, and therefore of the input signal to the dead timecontroller, DT_IN.

As shown in the timing diagram depicted in FIG. 13, the rising edge ofDT_LX is delayed, with respect to the falling edge of DT_HX, by a timeinterval of length t_(DHL), while the falling edge of DT_LX is advanced,with respect to the rising edge of DT_HX, by a time interval of lengtht_(DLH). This ensures a desired operation where no overlap between an ONstate of the HS control signal and an ON state of the LS control signalexist. Such desired operation in the exemplary embodiment depicted bythe associated timing diagram of FIG. 13 provides positive dead times(t_(DHL), t_(DLH)) at both transitions of the high side control signal.As mentioned above, there may be a desire to create a negative deadtime, in which case a person skilled in the art will recognize that therising and falling edges would be adjusted in opposite directions tothose described for the positive dead time control described herein andwith reference to FIG. 13.

Having described the overall function of dead time controller accordingto some embodiments of the present disclosure, an exemplary embodimentis now described in detail. Based on the timing diagram shown in FIG.13, a person skilled in the art will recognize that the dead timeadjusted signal DT_HX can be obtained, for example, by independentlydelaying leading (rising) and trailing (falling) edges of positivepulses of the DT_IN signal, and that the dead time adjusted signal DT_LXcan be obtained, for example, by independently delaying leading andtrailing edges of the positive pulses of the DT_IN signal followed byinverting the obtained delayed signal. Likewise, same delayingoperations may be performed on leading (falling) and trailing (rising)edges of negative pulses of the DT_IN signal to obtain the dead timeadjusted signals DT_HX and DT_LX.

FIGS. 14A and 14B show a basic edge delay circuit (1410) according to anembodiment of the present disclosure that can be used to generate thedead time adjusted signals DT_HX and DT_LX based on the DT_IN signal.FIG. 14A shows a positive pulse, POS_IN, processed by the basic edgedelay circuit (1410) and FIG. 14B shows a negative pulse, NEG_IN,processed by the basic edge delay circuit (1410). As can be seen in FIG.14A, the circuit (1410) takes the positive pulse, POS_IN, and outputs apositive pulse, POS_IN_(TE), which corresponds to the positive pulsePOS_IN with a delayed timing of the trailing edge and a substantiallysame timing of the leading edge. Likewise, as can be seen in FIG. 14B,the circuit (1410) takes the negative pulse, NEG_IN, and outputs anegative pulse, NEG_IN_(LE), which corresponds to the negative pulseNEG_IN with a delayed timing of the leading edge and a substantiallysame timing of the trailing edge.

The basic edge delay circuit (1410) achieves a trailing edge delay of apositive pulse input to the circuit and a leading edge delay of anegative pulse input to the circuit, while maintaining polarity(positive or negative) of the pulse input to the circuit. It followsthat cascading (series connecting) a plurality of such circuits, leadsto an output pulse having a same polarity as an input pulse and delayingof a same leading and/or trailing edge of the input pulse. The basicedge delay circuit (1410) comprises a transistor M00 that operates as ashunting switch having an ON and an OFF state. A falling edge of aninput pulse signal provided at the gate of the transistor M00, turns OFFthe transistor M00, and a rising edge of the input pulse signal turns ONthe transistor.

Considering the positive pulse signal, POS_IN, as shown in FIG. 14A, ata time prior to the leading (rising) edge, since the signal is at a lowlevel, the transistor M00 is turned OFF and therefore the capacitor C0is fully charged, keeping the voltage at node A, input of the inverterH01, above the trigger point of the inverter, and therefore the outputof the inverter H01 is at a low level (i.e., following the input pulsesignal, POS_IN). When the leading edge of the positive pulse signal,POS_IN, arrives, the transistor M00 turns ON, shorting out the capacitorC0 and causing the output of the inverter H01 to transition to a highstate (again following the input pulse signal, POS_IN). When thetrailing edge of the input pulse signal, POS_IN, arrives, the transistorM00 turns OFF and diverts the current from current source I0 intocapacitor C0, thereby charging up the capacitor at node A. Once thevoltage on the capacitor C0 reaches the trip point of the inverter H01,shown as a time delay of t_(TE) in the timing diagram of FIG. 14A, theinverter H01 switches its output state (voltage), thereby causing atransition of the trailing edge of the pulse POS_IN by the time delay,t_(TE). A person skilled in the art would clearly understand that thetime delay t_(TE) is determined by the ratio of the capacitor C0 to thecurrent I0, and the trip point of the inverter H01. Accordingly, asshown in FIG. 14A, the output pulse, POS_IN_(TE) maintains the polarityof the input pulse, POS_IN, and is lengthened with respect to the inputpulse, POS_IN, by the time delay t_(TE) induced in its trailing edge.

As can be seen in FIG. 14B, the leading (falling) edge of the negativepulse signal, NEG_IN, turns OFF the transistor M00 and diverts thecurrent from current source I0 into capacitor C0, thereby charging upthe capacitor at node A. Once the voltage on the capacitor C0 reachesthe trip point of the inverter H01, shown as a time delay of t_(LE) inthe timing diagram of FIG. 14B, the inverter H01 switches its outputstate (voltage), thereby causing a transition of the leading edge of thepulse NEG_IN by the time delay, t_(LE). A person skilled in the artwould clearly understand that the time delay t_(LE) is determined by theratio of the capacitor C0 to the current I0, and the trip point of theinverter H01. Once the trailing (rising) edge of the pulse NEG_INarrives, the transistor M00 is turned ON, thereby shorting out thecapacitor C0 and sinking the current from current source I0. This forcesthe remaining circuitry to pass the trailing edge without any extradelay as shown in the timing diagram of FIG. 14B. Accordingly, as shownin FIG. 14B, the output pulse, NEG_IN_(LE) maintains the polarity of theinput pulse, NEG_IN, and is shortened with respect to the input pulse,NEG_IN, by the time delay t_(LE) induced in its leading edge.

With further reference to the basic edge delay circuit (1410), it ispointed out that the operating conditions (e.g., threshold voltage andtemperature sensitivity) of the transistors of the current source I0 andthe transistor M00 should track the transistors of the inverter H01 toensure proper timing control. A person skilled in the art wouldappreciate that the basic edge delay circuit (1410) according to thepresent teachings comprises only high speed circuit elements includingtransistors, inverters, and capacitors, and is devoid of any seriesresistors that may negatively affect performance (e.g., speed). Deadtime controllers as known in the art rely on operational amplifiers orcomparators, which are slow, induce extra delays, and exhibit low slewrates (aka long transition times) as compared to an inverter. By usingthe basic edge delay circuit (1410) for generating the timing adjustedsignals DT_HX and DT_LX (e.g., per FIG. 13), high slew rate transitionsleading to accurate delays in the leading and trailing edges can beprovided, both of which are important characteristics as discussedbelow.

FIG. 15A and FIG. 15B show that coupling of one or more inverters to aninput and/or output of the basic edge delay circuit (1410) can providefurther flexibility to the basic edge delay circuit (1410), and notrestricting operation to leading edge delay for a negative input pulsesignal, trailing edge delay for a positive input pulse signal, and samepolarity of input and output pulses.

For example, as shown in the combined circuit of FIG. 15A, a leadingedge delay of a positive input pulse signal, POS_IN, can be obtained byreversing the positive polarity of the input signal via an inverter H02coupled to the input of the basic edge delay circuit (1410). As shown inFIG. 15A, the inverter H02 reverses the positive polarity of the inputsignal, POS_IN, by generating, therefrom, a negative pulse signal,/POS_IN, that is the inverted version of the positive input pulsesignal, POS_IN. Accordingly, the basic edge delay circuit (1410) delaysthe leading edge of the inverted signal, /POS_IN, which corresponds tothe leading edge of the positive input pulse signal, POS_IN, as shown inthe timing diagram of FIG. 15A (based on the timing diagram of FIG.14B). If desired, an inverter H03 coupled to the output of the basicedge delay circuit (1410) can be used to restore the polarity of thepositive input pulse signal, POS_IN. Accordingly, the inverter H02allows leading edge delay of a positive input pulse signal to the basicdelay circuit (1410), and the inverter H03 allows for a same positivepulse polarity at an input and output of the combined circuit.

Likewise, as can be seen in FIG. 15B and corresponding timing diagram,same combined circuit as shown in FIG. 15A can be used to provide atrailing edge delay of a negative input pulse signal, NEG_IN. It shouldbe noted that the inverter H03 is merely used to restore polarity of theinput pulse signal, and in some applications, may not be required.

Based on the above, it becomes clear to a person skilled in the art thatany one of a trailing edge or a leading edge of either of positive pulsesignal or a negative pulse signal can be adjusted by a combination ofthe basic edge delay circuit (1410) with one or more inverters coupledto its input and/or output.

As noted above, since the basic edge delay circuit (1410) preservespolarity of the input pulse signal, and since for a same input pulsepolarity, same edge is delayed by the basic edge delay circuit (1410),cascading (series connecting) a plurality of such circuits (1410)results in compounding a same edge delay. However, by inserting aninverter in the front of one of the cascaded basic edge delay circuits(1410), polarity of the signal is reversed and therefore a differentedge of the signal is delayed. This is shown in the exemplary dead timecontrol circuits (1600A, 1600B) of FIGS. 16A, 16B, wherein each of thetiming adjusted signals, DT_HX and DT_LX, is independently generatedaccording to a separate processing path comprising a number of cascadedbasic edge delay circuits (1410).

With further reference to FIG. 16A, a processing path of the timingadjusted signal DT_HX comprises two series connected basic edge delaycircuits (1410 a, 1410 b). A trailing edge of a positive pulse of theDT_IN signal can be adjusted (delayed) by the circuit (1410 a) accordingto the description above with reference to FIG. 14A. The inverter H12inverts the output of the circuit (1410 a) and therefore reversespolarity on the signal to the circuit (1410 b). In turn, the circuit(1410 b) adjusts (delays) the leading edge of the positive pulse of theDT_IN signal, according to the description above with reference to FIG.14B and FIG. 15A. The inverter H32 can be used to restore the polarityof the positive pulse of the DT_IN signal.

With continued reference to FIG. 16A, a processing path of the timingadjusted signal DT_LX comprises two series connected basic edge delaycircuits (1410 c, 1410 d). A trailing edge of the positive pulse of theDT_IN signal can be adjusted (delayed) by the circuit (1410 c) accordingto the description above with reference to FIG. 14A. Since the signal tothe next circuit (1410 d) is not inverted, then the circuit (1410 d) canapply another delay to the same trailing edge of the positive pulse ofthe DT_IN signal. This can extend the amount of the trailing edge delayof the processed output signal (DT_LX) to an amount that is beyond thecapability of a single basic edge delay circuit. If needed, the inverterH22 can be used to invert the output of the circuit (1410 a) andtherefore provide a desired polarity of the output signal, DT_LX. Aperson skilled in the art would clearly understand that same circuitshown in FIG. 16A can be described in terms of any of the positive pulse(a rising leading edge followed by a falling trailing edge) and negativepulse (a falling leading edge followed by a rising trailing edge) of theDT_IN signal (square wave), with same result in the output waveforms ofDT_HX and DT_LX

FIG. 16B shows a generic implementation (1600B) of a dead time controlcircuit according to an embodiment of the present disclosure, based on acascaded combination of one or more basic edge delays circuits (1410)and one or more inverters. As can be seen in FIG. 16B, a processing pathof the timing adjusted signal DT_HX comprises one or more seriesconnected basic edge delay circuits (1410 a 1, . . . , 1410 am) toadjust a trailing edge of a positive pulse of the DT_IN signal, and oneor more series connected basic edge delay circuits (1410 b 1, . . . ,1410 bn) which can be used to adjust a leading edge of the positivepulse of the DT_IN signal given presence of an optional inverter, H0 a.Another optional inverter H0 b can be used to either restore polarity ofthe output signal, DT_HX or switch its polarity to a desired polarity.Likewise, a processing path of the timing adjusted signal DT_LXcomprises one or more series connected basic edge delay circuits (1410 c1, . . . , 1410 ap) to adjust a trailing edge of a positive pulse of theDT_IN signal, and one or more series connected basic edge delay circuits(1410 d 1, . . . , 1410 dq) which can be used to adjust a leading edgeof the positive pulse of the DT_IN signal given presence of an optionalinverter, H0 c. Another optional inverter H0 d can be used to eitherrestore polarity of the output signal, DT_LX or switch its polarity to adesired polarity. Furthermore, as shown in FIG. 16B, optional invertersHa1, Hc1 may be used at an input of each of the two processing paths tofurther invert the input to each of the two processing paths, andtherefore establish an order of processing of the leading and trailingedges of the input signal through the two processing paths (e.g.,process with respect to negative pulses).

FIG. 17A shows a configurable edge delay circuit (1710A) according to anembodiment of the present disclosure that is based on the basic edgedelay circuit (1410) with added flexibility to selectively invert aninput to the basic edge delay circuit. As can be seen in FIG. 17A, aninput pulse, PULSE_IN, to the configurable edge delay circuit (1710A),and an inverted version of the input pulse, /PULSE_IN, that is invertedby way of an inverter, H02, are selectively routed to the input of thebasic edge delay circuit (1410) through a switch, SW01. This in turnallows operation of the configurable edge delay circuit (1710A)according to the operation of any of the configurations described abovewith reference to FIGS. 14A, 14B, 15A and 15B. In other words, theconfigurable edge delay circuit (1710) can selectively delay a leadingor trailing edge of any of a positive or negative polarity pulse.

FIG. 17B shows an alternative embodiment of a configurable edge delaycircuit (1710B), based on the configuration (1710A) described above withreference to FIG. 17A, with added flexibility with respect to theconfiguration (1710A) of FIG. 17A to selectively invert an output pulse,PULSE_OUT, of the configurable edge delay circuit (1710B). As can beseen in FIG. 17B, the output pulse, PULSE_OUT, is selected through aswitch (e.g., single-pole, double-throw), SW02, from one of an outputpulse to the basic edge delay circuit (1410) and an inverted version ofsuch output pulse that is inverted by way of an inverter, H03. Theinverter H03 can be selectively used to provide operation per theinverter H03 described above with reference to FIGS. 15A and 15B. Aperson skilled in the art would clearly understand that the addition ofthe inverters H02, H03 in an edge processing path as provided in theconfigurations 1710A, 1710B, as well as ones described above withreference to FIGS. 15A, 15B, 16A and 16B, may introduce a slight addeddelay of the edges but with no effect on relative timing of two parallelprocessing paths (e.g., HS and LS paths).

FIG. 18A shows an exemplary dead time control circuit (1800A) accordingto an embodiment of the present disclosure based on the configurableedge delay circuits (1710A) and/or (1710B), wherein edge timingprocessing for each of the dead time adjusted signals DT_HX and DT_LX isbased on two series connected (cascaded) circuits (1710A) or (1710B),denoted (1710A/B) in the figure. Based on the description above withreference to FIGS. 14A-17B, a person skilled in the art would appreciateflexibility in timing adjustment of the edges provided by the dead timecontroller (1800A). In particular, by controlling the configuration(e.g., via switches SW01 and SW02) of each of the two series connectedconfigurable edge delay circuits (1710A/B), any of the leading andtrailing edges of the input signal, DT_IN can be adjusted, and anypolarity of the output adjusted signal (DT_HX, DT_LX) with respect tothe polarity of the input signal can be obtained. For example, byappropriate setting of the switches (SW01, SW02) in the processing pathof each of the DT_HX and DT_LX signals, the configuration (1600A) ofFIG. 16A can be obtained. Other settings of the switches can allowdifferent configurations as necessary. Furthermore, by cascading aplurality of configurable edge delay circuits (1710A/B), as shown inFIG. 18B, further delaying of any or both of the falling and risingedges beyond the capability of a single configurable edge delay circuit(1710A/B) can be provided. In particular, any configuration based on avariation of the configuration (1600B) described above with reference toFIG. 16B can be provided.

A person skilled in the art would clearly appreciate the flexibility incontrolling of edge timing as well as signal polarity provided by theconfigurable edge delay circuit (1710A) and (1710B). According to anembodiment of the present disclosure, such configurable edge delaycircuit can be used as a building block of an edge timing controller(1800C) shown in FIG. 18C, which can be used in any application whereprecise control of edges of a square wave signal is desired. Operationand configuration of such edge timing controller should be clear to aperson skilled in the art based on the description above. The edgetiming controller (1800C) can generate edge and polarity adjusted outputsignals, PULSE_OUT1, . . . , PULSE_OUTn, based on a single input signal,PULSE_IN. As described above, either one or both of the falling andrising edges of each of the output signals, PULSE_OUT1, . . . ,PULSE_OUTn, as well as respective polarities with respect to the inputsignal, PULSE_IN, can be adjusted independently.

It is pointed out that any dead time control circuit according to thepresent teachings must ensure that, as shown, for example, in FIG. 12A,the HS and LS outputs are of inverted polarity, ensuring that HS and LSdevices T1, T2, are not intentionally on at the same time. In addition,all four edges (HS rising, HS falling, LS rising and LS falling) can bedelayed by adjusting the size of each of the current sources (e.g., I0of FIGS. 14A, 14B), each of which may be of any value (i.e., any of thecurrent sources may be of separate magnitudes). This allows for ensuringthe different timing signals can be adjusted relative to each other, andspecifically they can be adjusted to increase or decrease the relativetiming between them.

For example, HS rising edge can be delayed relative to LS falling edgeto ensure no timing overlap, causing so-called shoot through current,which wastes power and can damage other devices. Since timing at thefinal stages of an overall system can be affected by factors beyond thedead time control circuitry, such as circuit board delays or evenconnectors between boards, it may be necessary to cause a HS signal tooverlap a LS signal at the output of the dead time controller in orderto compensate other system delays. Being able to adjust timing of allfour edges, and to create either positive or negative overlap of pairededges is a unique capability of the current invention.

With reference back to the basic edge delay circuit (1410) shown inFIGS. 14A and 14B, according to an exemplary embodiment of the presentdisclosure, timing adjustment (e.g., delay) of an edge can be achievedby setting the value (magnitude) of the current source I0 either withon-chip or off-chip components. For example, a current mirrored currentsource (current DAC) can be a programmable way to adjust the currentsource I0. In such an example, digital programming, potentiallyincluding fuses, may be used to program the current DAC. An advantage ofthis approach is provision of a programmable timing adjustment based oncomponents that can be entirely found on the same chip along with thedead time control circuit. Setting of the value of the current sourcecan be provided via the control signals, CNTL, as shown in the abovedescribed FIG. 11.

According to an embodiment of the present disclosure, a magnitude of thecurrent source I0 of the basic edge delay circuit (1410) can also bechanged by adjusting an off-chip component such as a resistor (e.g.,resistor R of FIG. 19 later described). In such a case, the resistorvalue can be chosen for a given application and changed during circuitboard assembly. An advantage of this approach is to avoid the need foron-chip programming and it is typically a very inexpensive and accuratesolution.

According to a further embodiment of the present disclosure, timingadjustment can also be achieved by replacing the on-chip capacitor C00of the basic edge delay circuit (1410), shown as a fixed capacitor inFIGS. 14A and 14B, with digitally tunable capacitors, again offeringon-chip solutions with programmability. Alternatively, the capacitor C00can be off-chip and be adjusted on the circuit board level, just as forthe current source resistors described above. An exemplary digitallytunable capacitor is described in the above reference U.S. Pat. No.9,024,700 B2, the disclosure of which is incorporated herein byreference in its entirety.

According to a further embodiment of the present disclosure, timingadjustment of a dead time controller (1400A, 1400B, 1600A, 1600B), or anedge timing controller (1800C), described above, can be provided byincremental adjustment of the edges based on a plurality of cascadedbasic edge delay circuits (1410) and/or configurable edge delay circuits(1710A, 1710B), where each such circuit can perform a same or differenttiming adjustment. For example, coarse and fine adjustments can beprovided according to a weighing scheme of the timing adjustmentsprovided by each of the delay circuits (1410, 1710A, 1710B), whereindividual timing adjustments can be provided by way of any of themethods discussed above (e.g., resistor, capacitor, current source).

A person skilled in the art would clearly appreciate the numerousadvantages provided by the edge delay circuits according to the presentteachings, including:

Efficiency: With very sharp rise and fall times, thanks to use ofinverters rather than comparators or op amps, ON and OFF timing can beadjusted to very fine accuracy. Additionally, accurate elimination ofshoot through current also improves efficiency;

Low distortion: Accurate timing control at the final output, for examplea class D amplifier, ensures accurate, undistorted reproduction of theoutput drive signal as intended by the input signal;

High speed: High speed edges, again thanks to elimination of op amps andcomparators, enables high speed control which in turn enables very shortoutput pulses. This can enable high speed pulsed inputs as well as veryshort pulses;

Flexibility: All timing edges can be adjusted, creating both positiveand negative overlap of HS and LS signals. These edges can be adjustedwith either on-chip programmability or off-chip component placement.Various applications will benefit from these programming and adjustmentsoptions and a single chip can be used for (ie, programmed for) multipledifferent applications, saving inventory and purchasing costs;

Reliability: With accurate timing control and reduction of shoot-throughcurrents, output devices will operate at lower risk of damage.Additionally, increased efficiency reduces operating temperatures,thereby improving reliability;

and

Low cost: Flexibility, reliability, efficiency and single chipimplementation with off-chip component options all contribute to lowercost.

As known to a person skilled in the art, and discussed above, a trippoint associated with an inverter, such as the inverter used in any ofthe embodiment described above with reference to FIGS. 14A-18C, theinverter trip point, can change with a process (P) used to fabricate theinverter, as well as with a voltage (V) applied to the inverter (e.g.biasing, supply) and an operating temperature (T) of the inverter. Such“PVT” characteristics of the inverter can therefore affect operation ofthe edge delay circuits represented in FIGS. 14A-18C. It follows thataccording to an embodiment of the present disclosure, the current sourceI0 has an output current that is proportional to the trip point of theinverter (e.g., H01, H02, H03). It can be assumed that given a samefabrication process of such inverters, corresponding trip points remainthe same as a function of the PVT, since such inverters see a samebias/supply voltage (e.g. Vdd1) and are placed in a very close physicalproximity of each other and therefore subjected to a same localtemperature.

FIG. 19 shows a current source circuit 1900 according to a furtherembodiment of the present disclosure which can be used as the currentsource I0, and provide a current to the edge delay circuit according tothe present teachings that is compensated with respect to the PVT thatcauses a drift of the trip point of the inverter circuits (H01-H03).

In FIG. 19, an exemplary circuit is shown that ensures that the currentsource I0 is proportional to the inverter trip point, causing the impactof a variable trip point on time delay, as described above, to becancelled by the proportionally adjusted amount of current in currentsource I0. The exemplary circuit represented in FIG. 19 achieves this byusing a current mirror circuit (1710 a) (comprising a reference currentleg series connected with transistor M09, and one output mirrored legI0) which mirrors a current going through the transistor M09 and aresistor, R which can be an external resistor to the circuit (1900). Aperson skilled in the art will realize that such current is equal toVtrip of the inverter formed by M04 and M05 divided by the resistor, R.As the inverter (M04, M05) is representative of the inverters (H01-H03)used in the exemplary edge delay circuits according to the presentteachings, its trip point varies similarly to (tracks) the trip point ofsuch inverters.

More specifically, it is commonly known that the biased inverter shownin FIG. 19 formed by the transistors M04 and M05 and connecting thecommon drain node of the transistors to the common gate node of thetransistors, operates at its trip point (as inverter is biased at orclose to its trip point voltage), latter trip point voltage beingproportional to PVT as described above. This voltage serves as areference voltage for the operational amplifier OP1 which takes itsdriven voltage from the voltage on the external resistor, R. Due to thisfeedback, the operational amplifier OP1 forces the voltage on theresistor R to track the inverter (M4, M5) trip point voltage, andthereby forces the current through the resistor to track the PVT. Theknown current mirror (1710 a) depicted in FIG. 19 forces the current I0to match the current through the resistor R and thereby forces currentI0 to track the PVT.

The person skilled in the art readily understands that the variousteachings of the present disclosure can apply to multiple semiconductormaterials and device structures. For simplicity, the embodiments andexamples presented herein for illustrative purposes include only GaNFETs as the high voltage devices controlled by the gate driver circuit(e.g. HS level shifter) according to the various embodiments of thepresent disclosure, and SOI MOSFETs for the low voltage control devicesused in the gate driver circuit (e.g. HS level shifter). The personskilled in the art can use the teachings according to the variousembodiments of the present disclosure to derive level shifters andcontrols using other types of low voltage transistors (e.g. non SOIMOSFETs) and for interfacing with other types of high voltagetransistors (e.g. non GaN FETs).

As mentioned in the prior sections of the present disclosure, the levelshifter (e.g. HS level shifter (425)) according to the various presentedembodiments, as well as the gate driver circuit (410), can bemanufactured, either in its entirety or partially, in an integratedcircuit based on various technologies, and in particular in CMOS or SOICMOS. Again, as mentioned above, CMOS technologies, whether bulk Si orSOI, have high level of integration, ease of manufacturing and anassociated low cost. Furthermore, and as previously noted, low voltage(e.g. standard CMOS) transistors can have speed and performance whichcan drive GaN circuits (e.g. comprising high voltage GaN FETtransistors) in a manner that benefits from the low FOM of GaNtransistors.

However, while no transistor in the current level shifter (e.g. HS levelshifter (425)) withstands a high voltage across the transistor (e.g.across its drain and source), the overall circuit as described above(e.g. level shifter) floats to high voltage (e.g. with voltage at nodeSW) and therefore the entire circuit is isolated from GND and withstandsthe high voltage drop from V_(IN) to GND.

FIGS. 20A, 20B and 20C depict cross sections of the three main CMOSsemiconductor technologies, listed above, specifically, SOS, SOI andbulk Si, respectively. A person skilled in the art readily recognizesthat each of such cross sections shows a single P and a single N typetransistor, and that only the very basic features of the transistors areshown, e.g. their source, S; their drain, D; and their gate, G.

The cross section depictions in FIGS. 20A, 20B and 20C of the twotransistor types can be understood by a person skilled in the art torepresent any array of transistor circuitry. In each version of CMOSshown, the transistors, both P and N types, are low voltage transistorsas used in the level shifter (e.g. HS level shifter 425) of the presentdisclosure, e.g., they are capable of handling low source-drain voltagesof only, for example, 5 Volts, or less.

FIG. 20A shows an exemplary silicon on sapphire (SOS) structurecomprising two low voltage transistor devices (2110 a, P type) and (2120a, N type) each comprising a gate terminal (G), a drain terminal (D) anda source terminal (S), whose P+ and N+ drain and source regions areformed within a thin Si layer (2115) fabricated atop a sapphire (Al₂O₃)substrate (2125). While the low voltage transistors (2110 a) and (2110b) in FIG. 11A can only withstand low voltage, say up to 5V (between anytwo S, D, G terminals), an entire transistor circuit of the SOSstructure depicted in FIG. 20A can float from 0-V_(IN) volts withrespect to GND. According to an embodiment of the present disclosure,the backside of the SOS structure depicted in FIG. 20A, denotedBackside, can be connected to a DC voltage, such as 0V (GND), or leftunconnected (floating). In the case of the level shifter (e.g. HS levelshifter (425,) according to the present teachings, the reference voltagefor the level shifter circuitry (e.g. high side) is at Vss level (e.g.tied at common node SW), which is either 0 V (e.g. when the LS GaN FETT1 is ON), up to a voltage level of V_(IN) (e.g. when the HS GaN FET T2is ON). Therefore, as a person skilled in the art can recognize, the lowvoltage transistors (2110 a) and (2110 b) represented in FIG. 20A canoperate at a high voltage (e.g. equal to or larger than V_(IN), such asV_(IN)+Vdd2 as depicted in FIG. 4) with respect to GND without everhaving to handle any high voltage being impressed across them (e.g.across a corresponding source and drain). Instead, the sapphiresubstrate has the high voltage drop (e.g. V_(IN)+Vdd2) across its entirethickness. In a typical embodiment, the sapphire substrate (2125) may be10's to 100's of micrometers thick and therefore the electric fieldcreated by such high voltage is well below the well-known dielectricstrength of the sapphire.

FIG. 20B shows an exemplary silicon on insulator (SOI) transistorstructure comprising two low voltage transistor devices (2110 b, P type)and (2120 b, N type), each comprising a gate terminal (G), a drainterminal (D) and a source terminal (S), in which a thin Si layer (2115),which comprises the P+ and N+ source and drain regions of the P type andN type transistors, is formed on a buried silicon dioxide layer (2130),thence on a Si substrate (2140). As in the case of the SOS structure ofFIG. 20A, while the low voltage transistors (2110 b) and (2120 b) of thestructure depicted in FIG. 20B can only withstand up to, say, 5V(between any two S, D, G terminals), the entire transistor structure canfloat from 0-V_(IN) volts with respect to GND. According to anembodiment of the present disclosure, the backside of the SOI structuredepicted in FIG. 20B, denoted Backside, can be connected to a DCvoltage, such as 0V (GND), or left unconnected (floating). In the caseof the level shifter (e.g. HS level shifter (425) according to thepresent teachings, the reference voltage for the level shifter circuitry(e.g. high side) is at Vss voltage level, which is either 0 V (e.g. whenthe LS GaN FET T1 is ON) up to a voltage level of VIN (e.g. when the HSGaN FET T2 is ON). Therefore, as a person skilled in the art canrecognize, the low voltage transistors (2110 b) and (2120 b) representedin FIG. 20B can operate at a high voltage (e.g. equal to or larger thanV_(IN), such as V_(IN)+Vdd2 as depicted in FIG. 4) with respect to GNDwithout ever having that high voltage impressed across them (i.e. acrossany two constituent terminals S, D, G). Instead, the buried silicondioxide layer has the high voltage drop across its thickness. Suchburied silicon dioxide layer is clearly much thinner than the sapphiresubstrate in the SOS embodiment shown in FIG. 20A.

In a typical SOI embodiment, the Si layer (2115) and the buried silicondioxide layer (2130) can typically be 0.1-1.0 micrometers in thicknessand the Si substrate (2140) underneath the Si layer (2115) and theburied silicon dioxide layer (2130) can typically be 10's to 100's ofmicrometers thick. Therefore, the electric field inside the buriedsilicon dioxide layer (2130) can typically be higher than in thesapphire substrate case depicted in FIG. 20A (since typically thesapphire substrate is much thicker than the silicon dioxide layer andcan therefore withstand a much higher V_(IN) voltage). In a properlydesigned embodiment, the buried silicon dioxide layer (2130) is thickenough to withstand a maximum electric field associated to a voltageV_(IN) plus any noise spikes that may be impressed on the V_(IN)voltage, applied to the GND plane of the Si substrate (2140). It shouldbe noted that being able to withstand large electric field is not theonly issue for the thin silicon dioxide layer. The bottom Si layer alongwith the thin silicon dioxide layer can create a back-gate to both theNMOS and PMOS transistors. When both NMOS and PMOS transistors fly to ahigh voltage such as 100V, the back-gate of the PMOS device would turnON, similar to how the top gate turns ON the channel of the PMOS throughthe gate oxide. The NMOS in this case is not affected, but the PMOS inthis case cannot be shut off. The threshold voltage of this back gate istypically higher than that of the top gate by roughly the ratio of thethickness of the buried silicon diode layer to the thickness of the gateoxide. Some counter measures to such back gate effect may be theintroduction of S-Contacts in the SOI transistor structure of FIG. 20Bas described, for example, in the above referenced U.S. patentapplication Ser. Nos. 14/964,412 and 15/488,367, the disclosures ofwhich are incorporated herein by reference in their entirety.

FIG. 20C shows an exemplary bulk Si transistor structure comprising twolow voltage transistor devices (2110 c, P type) and (2120 c, N type),each comprising a gate terminal (G), a drain terminal (D) and a sourceterminal (S). A person skilled in the art readily knows that suchstructure is at least semiconductive throughout its entire thickness.Since Si is a good conductor relative to insulators such as silicondioxide or sapphire, the high voltage V_(IN) must be dropped acrosscorresponding reverse-biased diodes of such bulk Si structure that havehigh enough stand-off voltage to provide isolation to the grounded Sisubstrate. In the exemplary structure depicted in FIG. 20C, the highvoltage, V_(IN), is dropped across the diode formed by the bottomN-wells (N-WELL-1 and N-WELL-2) and the p-type substrate. This is shownin FIG. 20C for the typical case where V_(IN) is positive, where N-WELL1and N-WELL2 are connected, via an associated terminal (2112), to node SWwhich swings form 0 (GND) to V_(IN). The person skilled in the artreadily knows that for the case where V_(IN) is negative, polarities ofthe structures shown in FIG. 20C can be reversed (e.g. all P structuresto N structures and vice versa, including reversal of the p-Si substrateto n-Si substrate) in order to allow the bulk p-Si substrate, which isgrounded on its back side (e.g. connected to GND), to handle a largenegative voltage drop (V_(IN)<0V). In such case where V_(IN) isnegative, node SW can be connected to P-WELLS provided within the n-Sisubstrate (connection not shown in FIG. 20C). The person skilled in theart readily knows that other well structures can be used in a Sistructure as long as such wells can provide high voltage handlingcapability equal to or larger than V_(IN) (e.g., V_(IN)+Vdd2 as depictedin FIG. 4). Again, while the low voltage transistors in the structuredepicted in FIG. 20C can only withstand up to, for example, 5V, theN-wells can float from 0-V_(IN) volts with respect to GND. It should benoted that the various structures and wells depicted in FIG. 20C are notto scale, including the horizontal spacing between the two N-wells whichmust be large enough to provide lateral isolation between the wells.

Unlike insulators such as silicon dioxide or sapphire, diodes in bulk Sistructures can block current only in one direction, therefore asdescribed above, the exemplary transistor structure depicted in FIG. 20Cused in a level shifter (e.g. HS level shifter (425) according to thevarious embodiments of the present disclosure can work for cases whereV_(IN)>0V (=GND), or, by using an alternate wells structure (e.g.reverse polarity structures), for cases where V_(IN)<0V. Theinsulator-based transistor structures depicted in FIGS. 20A and 20B canhandle both positive and negative values of V_(IN), and can therefore beused in a level shifter according to the various embodiments of thepresent disclosure where V_(IN) takes either or both positive andnegative values. Since bulk Si structures can be cheaper, however, it isvaluable to note that while the insulator-based solutions may havesuperior performance or flexibility, the bulk Si solution may havereduced cost.

FIG. 21 is a process chart (2100) showing various steps of a method forcontrolling a high voltage device capable of withstanding a voltagehigher than a first voltage with low voltage devices capable ofwithstanding a voltage equal to or lower than a second voltage, thefirst voltage being substantially higher than the second voltage,according to an embodiment of the present disclosure. As can be seen inthe process chart (2100), the method comprises: providing a plurality oflow voltage devices configured to withstand a voltage equal to or lowerthan the second voltage, per step (2110); operating the plurality of lowvoltage devices between a first switching voltage (SW) and a secondswitching voltage (Vdd2+SW), the first switching voltage switchingbetween a reference voltage (GND) and the first voltage, and the secondswitching voltage substantially corresponding to a sum of the firstswitching voltage and the second voltage (per step 2120); generating twocomplementary pulse signals based on an input signal, the twocomplementary pulse signals comprising a first input timing controlpulse signal and a second input timing control pulse signal that is aninverted version of the first input timing control pulse signal, perstep (2130); coupling the first and second input timing control pulsesignals to the plurality of low voltage devices via a respective firstand second parallel resistive-capacitive couplings, per step (2140);based on the coupling, transmitting edge information and DC levelinformation of the first and second input timing control pulse signalsto the low voltage devices, per step (2150); based on the operating andthe transmitting, generating, via the plurality of low voltage devices,an output timing control signal at a voltage higher than the firstswitching voltage, per step (2160); and based on the generating,controlling the high voltage device, per the last step (2170).

With this semiconductor description, an innovative apparatus for biasingand driving high voltage semiconductor devices using only low(breakdown) voltage transistors has been disclosed. Prior artshortcomings related to loss of timing information due to high voltageswitching events have been addressed by way of inclusion of a parallelresistive-capacitive coupling that may pass edge information and DClevel information of a pulse signal representative of timing controlinformation for the high voltage semiconductor devices from one (static)voltage domain to a flying voltage domain. An innovative flyingcomparator with clamping, provided via low voltage transistors, alongwith logic circuit around a latch according to the present teachingscreates a filter-like block that removes unwanted glitches during aswitching event.

Applications that may include the novel apparatus and systems of variousembodiments include electronic circuitry used in automotive, batterysystems, solar power systems, high voltage audio systems, high-speedcomputers, communication and signal processing circuitry, modems, singleor multi-processor modules, single or multiple embedded processors, dataswitches, and application-specific modules, including multilayer,multi-chip modules. Such apparatus and systems may further be includedas sub-components within a variety of electronic systems, such astelevisions, cellular telephones, personal computers (e.g., laptopcomputers, desktop computers, handheld computers, tablet computers,etc.), workstations, radios, video players, audio players (e.g., mp3players), vehicles, medical devices (e.g., heart monitor, blood pressuremonitor, etc.) and others. Some embodiments may include a number ofmethods.

The term “MOSFET”, as used in this disclosure, means any field effecttransistor (FET) with an insulated gate and comprising a metal ormetal-like, insulator, and semiconductor structure. The terms “metal” or“metal-like” include at least one electrically conductive material (suchas aluminum, copper, or other metal, or highly doped polysilicon,graphene, or other electrical conductor), “insulator” includes at leastone insulating material (such as silicon oxide or other dielectricmaterial), and “semiconductor” includes at least one semiconductormaterial.

As should be readily apparent to one of ordinary skill in the art,various embodiments of the invention can be implemented to meet a widevariety of specifications. Unless otherwise noted above, selection ofsuitable component values is a matter of design choice and variousembodiments of the invention may be implemented in any suitable ICtechnology (including but not limited to MOSFET structures), or inhybrid or discrete circuit forms. Integrated circuit embodiments may befabricated using any suitable substrates and processes, including butnot limited to standard bulk silicon, silicon-on-insulator (SOI), andsilicon-on-sapphire (SOS). Unless otherwise noted above, the inventionmay be implemented in other transistor technologies such as bipolar,GaAs HBT, GaN HEMT, GaAs pHEMT, and MESFET technologies. However, theinventive concepts described above are particularly useful with anSOI-based fabrication process (including SOS), and with fabricationprocesses having similar characteristics. Fabrication in CMOS on SOI orSOS enables low power consumption, the ability to withstand high powersignals during operation due to FET stacking, good linearity, and highfrequency operation (i.e., radio frequencies up to and exceeding 50GHz). Monolithic IC implementation is particularly useful sinceparasitic capacitances generally can be kept low (or at a minimum, keptuniform across all units, permitting them to be compensated) by carefuldesign.

Voltage levels may be adjusted or voltage and/or logic signal polaritiesreversed depending on a particular specification and/or implementingtechnology (e.g., NMOS, PMOS, or CMOS, and enhancement mode or depletionmode transistor devices). Component voltage, current, and power handlingcapabilities may be adapted as needed, for example, by adjusting devicesizes, serially “stacking” components (particularly FETs) to withstandgreater voltages, and/or using multiple components in parallel to handlegreater currents. Additional circuit components may be added to enhancethe capabilities of the disclosed circuits and/or to provide additionalfunctional without significantly altering the functionality of thedisclosed circuits.

A number of embodiments according to the present disclosure have beendescribed. It is to be understood that various modifications may be madewithout departing from the spirit and scope of such embodiments. Forexample, some of the steps described above may be order independent, andthus can be performed in an order different from that described.Further, some of the steps described above may be optional. Variousactivities described with respect to the methods identified above can beexecuted in repetitive, serial, or parallel fashion.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the disclosure, which isdefined by the scope of the following claims, and that other embodimentsare within the scope of the claims. (Note that the parenthetical labelsfor claim elements are for ease of referring to such elements, and donot in themselves indicate a particular required ordering or enumerationof elements; further, such labels may be reused in dependent claims asreferences to additional elements without being regarded as starting aconflicting labeling sequence).

1. (canceled)
 2. A level shifter, comprising: low voltage transistordevices configured to operate between a first voltage and a secondvoltage; a first terminal configured to carry the first voltage; asecond terminal configured to carry the second voltage substantiallycorresponding to a sum of the first voltage and a low voltage; inputnodes configured to receive input timing control signals; a parallelresistive-capacitive network coupled between the input nodes and the lowvoltage transistor devices; and an output node configured to provide anoutput timing control signal, the output timing control signal beingbased on signal information of the input timing control signals throughthe parallel resistive-capacitive network.
 3. The level shifter of claim2, wherein the first voltage is equal to or higher than 10 volts, andthe low voltage is equal to or lower than 5 volts.
 4. The level shifterof claim 2, wherein the first voltage is equal to or higher than 25volts, and the low voltage is equal to or lower than 2.5 volts.
 5. Thelevel shifter of claim 2, wherein the low voltage transistor devices areconfigured to withstand a voltage that is equal to or lower than the lowvoltage.
 6. The level shifter of claim 2, wherein the output timingcontrol signal is at a voltage that is higher than the first voltage. 7.The level shifter of claim 2, wherein the low voltage is substantiallylower than the first voltage.
 8. The level shifter of claim 2, whereinthe input nodes comprise two input nodes, each configured to receiveedge information and DC level information of the input timing controlsignals.
 9. The level shifter of claim 2, wherein: the parallelresistive-capacitive network comprises two parallel resistive-capacitivenet-works, each coupled to: i) a respective one of the two input nodesfor receiving a respective one of two complementary input timing controlsignals, and ii) a respective one of two common nodes coupled to the lowvoltage transistor devices.
 10. The level shifter of claim 2, wherein:the parallel resistive-capacitive network comprises a resistiveconduction path comprising one or more series connected resistors and acapacitive conduction path comprising one or more series connectedcapacitors.
 11. The level shifter of claim 2, wherein the level shifterfurther comprises: a capacitor that is coupled between a node that iscommon to the parallel resistive-capacitive network and to the lowvoltage transistor devices, and the second terminal; and a resistor thatis coupled between said node and the second terminal.
 12. The levelshifter of claim 11, wherein the level shifter further comprises: acapacitor that is coupled between the node that is common to theparallel resistive-capacitive network and to the low voltage transistordevices, and the first terminal; and a resistor that is coupled betweensaid node and the first terminal.
 13. The level shifter of claim 2,wherein the low voltage transistor devices comprises a plurality of lowvoltage transistor devices that are configured to operate as a flyingcomparator, the flying comparator comprising: differential input nodescoupled to the parallel resistive-capacitive network; and complementaryoutput nodes.
 14. The level shifter of claim 13, wherein the low voltagetransistor devices further comprises a plurality of low voltagetransistor devices that are configured as clamp circuits to limit aninstantaneous voltage across nodes of the plurality of low voltagetransistor devices of the flying comparator during a switching event ofthe first voltage.
 15. The level shifter of claim 2, further comprisinga charge pump circuit configured to amplify the input timing controlsignals.
 16. A level shifter, comprising: low voltage transistor devicesconfigured to operate in a flying voltage domain defined by a firstvoltage and a low voltage; input nodes configured to receive inputtiming control signals; a parallel resistive-capacitive networkconfigured to couple the input nodes and the low voltage transistordevices; and an output node configured to provide an output timingcontrol signal, the output timing control signal being based on signalinformation of the input timing control signals through the parallelresistive-capacitive network.
 17. The level shifter of claim 16, whereinthe low voltage transistor devices are configured to withstand a voltagethat is equal to or lower than the low voltage, the low voltage beinglower than the first voltage.
 18. A high voltage switching devicecomprising the level shifter of claim
 16. 19. The high voltage switchingdevice of claim 18, further comprising a high voltage transistor deviceconfigured to withstand the first voltage, wherein operation accordingto an ON mode and an OFF mode of the high voltage transistor device iscontrolled by the level shifter.
 20. The high voltage switching deviceof claim 19, wherein during the ON mode of operation, a voltage at asource terminal of the high voltage transistor device is substantiallyequal to the first voltage, and during the OFF mode of operation, avoltage at the source terminal of the high voltage transistor device issubstantially equal to a reference voltage.
 21. A DC/DC converter forconversion of a high DC voltage to a low DC voltage comprising the highvoltage switching device of claim
 19. 22. A method for controlling ahigh voltage device, the method comprising: providing a plurality of lowvoltage devices configured to withstand a voltage equal to or lower thana low voltage; operating the plurality of low voltage devices in aflying voltage domain defined by a first voltage and the low voltage,the first voltage higher than the low voltage; coupling input timingcontrol signals to the plurality of low voltage devices via a parallelresistive-capacitive network; based on the coupling, transmitting signalinformation of the input timing control signals to the low voltagedevices; based on the operating and the transmitting, generating, viathe plurality of low voltage devices, an output timing control signal ata voltage higher than the first voltage; and based on the generating,controlling the high voltage device.